Sleep. It’s the place where we’re all Vikings. Or donuts. Whatever it is that happens to you in your dreams. It’s the most horizontal you can be in a day, and it’s usually pretty relaxing. Man, who doesn’t love a good sleep? But what happens if you don’t get enough of it?

Everyone’s probably pulled an all-nighter at some point in their lives, whether for work or pleasure. You stay up all night, the morning comes around, you just figure “oh well. Been up this long, might as well stay up for a whole day.” 

At some point, though, that gets old. Usually we don’t go beyond a day or two at the most. And it’s fairly well known that at some point, you’ll start suffering some ill effects from not getting sleep.

The mechanics of how this works are not as well known, however. Nor is it always really clear exactly what goes wrong when you don’t get enough sleep, or just how bad things can get for you. So let’s take a look at what medical science tells us about sleep, how much you need, and what you’re risking if you don’t get enough. 

How Much Sleep Do You Need?

Most of the world seems to be based around the idea that we need 8 hours of sleep per night. We’ve divided our 24 hour periods into 8-hour segments as adults in the western world. You work for 8 hours you sleep for 8 hours and the other 8 hours is when you fit in everything else you need to do.

Realistically, it’s not always that simple. Medically speaking, as an adult, you should be getting at least 7 hours of sleep per night. The younger you are the more sleep you’re going to need. Babies are out there living the high life getting a recommended 16 hours of sleep per day. They’re basically cats until they’re a year old.

Hours of sleep is not a blanket thing, however. People are different and you can’t say specifically that everyone needs this many hours. Some people can function on less sleep, and some people are going to need more. In general, it’s the quality of your sleep that you need to be concerned about, as opposed to how much of it you get.

Sleep quality is concerned with how well you slept, rather than how long. Some nights you hit the pillow, you’re out like a light, and you wake up with your alarm in the morning. Ideally, you feel refreshed, and ready to start your day. That was a good, quality night’s sleep.

On the other hand, sometimes you lay down and you stare at your ceiling, you stare at the display on your clock; you toss and turn; you wake up three times to go to the bathroom, and in the morning you somehow feel worse than you did when you went to bed the night before. You could have had the exact same number of hours, but that was not quality sleep.

If you’re getting good sleep, you probably don’t need more than 9 hours as an adult. That’s not to say anything bad is going to happen to you if you sleep from 12:00 to 12:00 on a Sunday, it’s just that you probably won’t get a ton of benefit from those extra hours. 

How Long Can You Go Without Sleep?

In 1986 a man named Robert McDonald broke a world record by staying awake for nearly 19 consecutive days. His total hours was just below 454. That’s a hell of a long time to be awake and it’s generally not recommended. He had to be monitored the entire time and, as you might expect, people had to observe him non-stop to make sure he didn’t fall asleep. 

You can start feeling the effects of sleep deprivation after as little as 24 hours. Sleep deprivation has been likened to drunkenness. Going without sleep is like having a blood alcohol level of 0.1%. in most places in the world, that’s above the legal limit. That means you’re going to be suffering some cognitive impairments, slow reaction time, brain fog, all that stuff. The symptoms are all very similar to drunkenness. 

In addition to those various impairments, your stress hormone production actually begins to go up. So you’re going to start producing more cortisol and adrenaline. This is because your body knows you’re lacking sleep and trying to help you out.

By 36 hours of not having sleep, you’ll start having physical symptoms. They may not be obvious from the outside, but you’ll be suffering from hormone imbalances. Your appetite and body temperature can suffer, and your mental state will continue to deteriorate. Irritability is a very common symptom.

After two days of not having sleep, you can start experiencing something called microsleep. That happens when you’re still trying to stay awake but your brain has had enough of your shenanigans and actually shuts off for several seconds. You may not even notice it happens, and it’s like a little reset switch went off for less than a minute.

You’ll begin to notice some serious symptoms within three or four days of not sleeping. This can include hallucinations, paranoia, and even psychosis. Interestingly, there isn’t a ton of research on what happens when you stay awake this long because it’s not considered ethical to make someone do it. At this point, sleep deprivation is essentially torture, and your average doctor doesn’t want to do that to a patient. At least not in a way that would allow them to write about it in a scholarly journal after the fact.

We do know that your hallucinations can become longer and more complex at this level. It’s hard to speak without slurring, even walking without stumbling around is difficult. And by 120 hours you can experience psychotic breaks with reality.

But, just like not everyone needs the same amount of sleep, not everyone’s going to have the same experiences. The world record holder for sleep deprivation suffered very few ill effects from his experience, so your mileage may vary. As a general rule though, you probably don’t want to try it yourself.

Sleep Deficiency and Deprivation

A lack of proper sleep can manifest itself as either sleep deficiency or sleep deprivation. The terms are similar enough that you might want to use them interchangeably, but there is a technical difference between the two. Sleep deprivation could be considered more acute while sleep deficiency is more of a chronic issue. Sleep deprivation is one factor or symptom of sleep deficiency.

Additionally, sleep deficiency might involve sleep disorders that affect the way you sleep, the inability to get to sleep when you want to, or consistently poor-quality sleep.

About 1 in 5 people in America get less than 5 hours of sleep per night which qualifies a sleep deprivation. That’s essentially an epidemic. Your bad sleep can be caused by a number of things, some of which are in your control and some of which aren’t.

Sleeping at night can be hard if you take naps during the day. This throws off your natural cycle. Likewise, using devices like phones before bed has been shown to cause poor sleep. Caffeine and other drugs can affect your ability to get good, consistent sleep as well. All of this contributes to sleep deprivation which can spiral into sleep deficiency if it’s allowed to keep happening.

What Happens Physically When You Don’t Sleep

We briefly looked at what happens when you don’t get enough sleep, at least in general terms. Now let’s get a little more specific about what’s going to happen to your mind and body if you find yourself suffering from sleep deprivation for too long.

When you suffer from a lack of sleep, and that doesn’t mean not sleeping at all, that just means not getting the full, proper amount of sleep you need, you can expect that it will affect your mood the next day. There’s a good chance you’re going to be more irritable and experience other negative feelings but you otherwise or shouldn’t be affected by. You’ll also be feeling stress more acutely. 

People who did not have depression before developing sleep disorders have nearly double the risk of developing depression as those who don’t have sleep disorders. As many as 80% to 90% of people with depression suffer from insomnia. The effect on your mental health really can’t be overstated.

Poor sleep will also affect both your memory and ability to learn. In fact, your ability to learn new things can be reduced by as much as 40% if you’re not getting the proper sleep. This ironically flies in the face of the idea of a college student pulling an all-nighter to study for an exam, as you’re actually working against yourself at this point.

Just one night of sleep deprivation could affect both your balance and coordination making you clumsier and slower to react during the day. You literally walk differently when you haven’t had enough sleep.

There are also noticeable, physical tolls of not sleeping properly. Your immune system will suffer from a lack of sleep and that means you are more likely to get sick and stay sick longer. Even a simple cold is going to hit you harder and last longer when you suffer from sleep deprivation.

We have probably all seen somebody and thought they looked tired, and there’s a reason for that. You literally look different when you’re not getting enough sleep. You’re more likely to have puffy, red, or drooping eyes. Dark circles, pale flesh, and a drooping mouth were all noted as well. And because sleep affects cortisol levels, a lack of sleep could lead to more wrinkles. 

A lack of sleep has also been linked to weight gain. The same regions of your brain that are stimulated by smoking marijuana that can lead to the munchies are stimulated when you don’t get enough sleep. That means you’re inspired to eat more when you sleep less which can lead to obesity.

A lack of sleep later in life can also lead to dementia and Alzheimers. It can also put you at risk of hypertensive heart disease. Basically, sleep deprivation is bad for you across the board. There aren’t a lot of areas of your personal health that are going to improve if you’re not sleeping, but there are plenty that are going to get worse.

Arguably, the most Insidious thing about this is that it’s a game of inches. Each of these things grows slowly. So nothing is affected terribly at first, it’s just many little things chewing away at your overall health to make you feel worse in a way that’s really hard to even notice at first.

Can Lack of Sleep Kill You?

There are two ways to look at this question. If you fail to go to sleep for a long time, it’s not like your body is just going to seize up and you’re going to crap out. Lack of sleep isn’t like a gunshot wound. Lack of sleep has never directly killed anyone that we’re aware of. That said, chronic sleep deprivation can lead to accidents and earlier death. And there is evidence of lack of sleep being lethal to animals. 

There is actually a genetic condition called fatal familial insomnia which can develop over time and increase in severity the longer it goes. As it progresses mental and physical deterioration occur, including a breakdown of your body’s autonomic systems. Your ability to regulate your breathing and heart rate can suffer and that can ultimately be fatal to those who suffer from it. This is, of course, different from simply not getting enough sleep and suffering a fatal result.

Sleeping is normally a peaceful activity. When we retire to bed at night, most of us do not feel the need to bolt the doors and hide the keys. Nor do we padlock the fridge or lock away sharp objects. But for the one percent of the adult population who regularly sleepwalk (e.g. at least twice per month), closing your eyes at night can be a strange and sometimes terrible thing.^[1]

Although most sleepwalkers will just wander aimlessly around the house, embarrassing their families before finally slipping back into bed, some people do some very strange things indeed.

10 Have Sex

Sexsomnia is a condition which causes people to engage in sex acts in their sleep. Without being aware of it, sufferers can engage in sex alone or with a partner and never remember it when they wake up. Both men and women experience the condition, though it is more common in men.^[2]

Sexsomnia can be a particularly dangerous condition, both for the sufferer and those around them, as they are unable to comprehend issues of consent. In 2007, a jury cleared a Royal Air Force aircraft mechanic of rape after hearing that he suffered from sexsomnia. Kenneth Ecott climbed naked on top of an unconscious girl after a drunken party. The jury accepted that he had been in a state of “automatism” when he raped her.

There have been a number of sexsomnia defenses to rape charges, not all of them successful, and there have been attempts to outlaw the defense, albeit with little success. However, it seems juries are unlikely to acquit unless the defendant is able to prove that they had documented evidence of parasomnias prior to being charged with rape.

9 Drive

Just as people walk in their sleep, so it is possible for them to drive. Sleep drivers can often travel significant distances in their sleep. It is not known how common this is, nor how many road accidents are caused by somnambulists. It is likely that while sleepwalkers master the mechanics of driving, they will not be able to use higher skills such as navigation and will merely be driving on autopilot.^[3]

And of course, not only can sleepwalkers drive, but they can also drink and drive. In 2012, UK resident Becky Mason had a friend over at her place and drank several glasses of wine before going to bed. Afterward, she drove 8 kilometers (5 mi) to her office in her pajamas, only to be told by a bemused security guard that it was Saturday night and that she wasn’t due in work until Monday morning. She got back in her car to drive home and promptly crashed into a lamppost. Her blood-alcohol level was three times the legal limit.

At her trial, the security guard was a crucial witness in her defense, and she was acquitted of drunk driving on the grounds of automatism. After this debacle, she made sure to hand her car keys to her roommates every night, just in case.

8 Kill

In 2009, Brian Thomas of Wales was acquitted of the murder of his wife after he strangled her while sleepwalking. Thomas had suffered from night terrors for 50 years and usually slept in a separate room from his wife, but they had gone on vacation and were sharing a bed in their camper van.

Thomas usually took tablets for depression, which helped alleviate the symptoms, but stopped taking them while on the trip because they reduced his libido. They had enjoyed a pleasant evening, only slightly marred by a gang of young men racing cars near their van.

Not long after they fell asleep, Thomas had a nightmare that the youths had broken into the camper van, and he dreamed that he was defending his wife from their attack. Tragically, he was, in fact, strangling her. Thomas made a confused emergency call some time later, saying that he had strangled his wife in his sleep.

There have been other cases of sleepwalkers, usually men, killing in their sleep. Not unnaturally, their victims are usually their partners. In 1845, Albert Tirrell was the first person to successfully use the sleepwalking defense in the United States, after he killed his “mistress” and set fire to the brothel they were sleeping in.

One of the most controversial acquittals was that of Kenneth Parks, who, in 1987, drove 20 kilometers (12 mi) from his home to that of his in-laws, beat his mother-in-law to death, and tried to strangle his father-in-law. He then climbed back into his car and drove to the nearest police station and turned himself in. The case caused controversy mainly because Parks had financial problems caused by his gambling addiction. He had recently lost his job as a result of embezzlement. Subsequent examinations by sleep researchers, however, showed that his sleep was highly disturbed, which, when combined with the stress of the discovery of his gambling addiction, was enough to cause a violent sleepwalking episode with such tragic results.^[4]

7 Get Naked

Finding yourself naked in public is a common anxiety dream, but for many sleepwalkers, it can turn into reality.

Indeed, it has become so common that one hotel chain has even trained its staff on how to deal with the naked sleepwalkers who wander up and down its corridors. The problem appears to be almost exclusively male (in the hotels, at any rate), with confused guests turning up at the reception desk in their birthday suits to request a wake-up call or try to check out. Staff now keep towels on hand in order to preserve their guests’ modesty and master keys in order to guide them gently back to their rooms.^[5]

It is thought that stress probably increases the likelihood of a sleepwalking occurrence, and alcohol or unfamiliar surroundings can exacerbate it and lead to further confusion. Sleepwalkers may believe that they are at home or that they have stepped into the bathroom or even onto a private balcony, when in reality, they are wandering the halls in the altogether.

6 Talk (Too Much)

Almost everyone talks in their sleep at some point. However, some people hold entire conversations with themselves. Sleeptalking, or somniloquy, might seem like complete gibberish to those who are awake but appear perfectly logical to the sleepwalker. Though somniloquy is unlikely to cause serious harm, it can often prove embarrassing for sufferers.

Sleeptalking can run in families. It can be exacerbated by sleep deprivation, stress, and drug and alcohol use.^[6] Researchers have discovered that a lot of sleeptalk consists of negative words, such as “no,” and rather a lot of swearing.

Most sleeptalkers, it seems, are fairly foul-mouthed, but despite what the movies will have us believe, people do not tend to blurt out their darkest secrets in their sleep. There is no evidence that what sleepers are talking about is founded in fact. Indeed, in 2001, the Supreme Court in Massachusetts overturned a conviction of indecent assault when they found that the original jury had been prejudiced after hearing that one of the children in the case “disclosed” his abuse in his sleep.

5 Get Creative

Perhaps there is something about being unconscious that stirs the creative juices. In 2015, a 13-year-old girl was filmed playing the piano in her sleep. Though she could clearly be heard snoring and rested her head against the upright piano, she still managed to knock out a tune.

Sleepwalkers have also participated in the fine arts. Lee Hadwin has made a career selling paintings that he creates in his sleep. He claims to be unable to draw when he is awake but produces artworks in the middle of the night without ever remembering it in the morning. Though critics are divided about whether his work constitutes “real art” or just “doodling,” he has nevertheless sold his work to buyers all over the world, including to well-known aesthetes like Donald Trump.^[7]

Though most art experts believe that true art requires the artist to be both conscious and responsive, it seems it is possible for the brain to perform some creative functions while the artist is asleep.

4 Live The Dream

For most people, having a dream come true is usually a good thing. For those with REM behavior disorder (RBD), however, it could mean something entirely different.

Usually, when we enter REM sleep, our brain shuts off communication with our muscles, except those in our eyes and diaphragm (which allows us to breathe), effectively paralyzing us as we sleep. REM sleep usually comes in cycles of around 90 minutes, so dreamers will typically experience three or more cycles per night.

When RBD sufferers enter the REM stage of sleep, their muscles are not adequately paralyzed, and they act out their dreams. This may include violence, laughing, or reenacting movements made during the day, such as packing imaginary suitcases. Sometimes, sleepwalkers will jump out of bed or run around the house.^[8]

Because the only reality that the sleeper recognizes is the one in the dream, sufferers can injure themselves in real life without feeling it in the dream and without waking up. It’s kind of like The Matrix in reverse.

3 Commit Armed Robbery

In 2007, Maria Hudson fell asleep in front of the TV. Then she put on some pink rubber kitchen gloves and pulled a pair of tights over her head. She walked for ten minutes to her local convenience store, where she pulled out a 30-centimeter (12 in) kitchen knife and yelled, “Hand over your money!” in a tone much like that used by Brad Pitt in the film she had just been watching.

She only woke up when she was pinned to the shop floor by two police officers as they disarmed her. Hudson had no recollection of what happened, but medical experts believed that her “insane automatism” was brought on by her epilepsy.

Although a relative of the shop owners suffered a slashed wrist in the attack, his injury was, thankfully, not life-threatening. He recalled, “She was covered in my blood but didn’t say anything. Then when police arrived she suddenly seemed to come alive.” Hudson was acquitted after a trial.^[9]

2 Eat

People with sleep-related eating disorder (SRED) may have a perfectly healthy relationship with food during the day. But in their sleep, they will binge on foods that they would not eat while awake. It is common for SRED sufferers to stuff themselves with thick and high-sugar-content foods such as peanut butter or syrup, stuffing it all down very quickly before going back to bed without waking. Not only do they eat, but sufferers often cook, too, which can lead to knife injuries and burns.^[10]

Sleepwalkers can rustle up anything from a sandwich to a three-course meal. However, though they may appear to be awake, they are unlikely to be fully aware of which ingredients they are using, so eating the food that they have prepared may not always be a good idea.

SRED can have a serious effect on health. One obvious consequence is likely to be weight gain. Some sufferers try to cure themselves of binge-eating by ridding the house of high-calorie foods, but they may end up eating other, more dangerous things instead. Sleep-eaters have been discovered eating coffee grounds, bacon rinds, and paper and drinking poisonous fluids like bleach.

On the whole, it seems that stocking the fridge with chocolate is safer.

1 Balance (On Top Of A Crane)

One night in 2005 in London, a passerby spotted a young girl on the arm of a crane, 40 meters (130 ft) above the ground. Thinking that he was witnessing a suicide attempt, he alerted emergency services. It was only when a firefighter crawled toward her that it was discovered that she was asleep.

Responders were concerned that a rescue attempt might wake her. The 15-year-old had apparently walked from her home, climbed up the crane, and walked across the narrow beam in her sleep. Eventually, rescuers recovered her mobile phone and contacted her parents. They were able to phone and wake her gently, while firefighters positioned themselves to catch her if she fell.

Though the girl had managed to climb the crane in her sleep, it took a crew of firefighters with a hydraulic lift two and a half hours to bring her back down.^[11]

Ward Hazell is a writer who travels, and an occasional travel writer

As far as we know, every animal must rest at some point. We didn’t used to think so. Some animals, like the dolphin or bullfrog, simply have sleep habits that look an awful lot like not sleeping to the human eye.

But even those that don’t sleep at all still rest. Most insects enter into a state called torpor, which significantly reduces their awareness. Even bacteria have been shown to follow a circadian rhythm, cycling through different levels of activity based on changes in the light.

Sleep is still somewhat mysterious to us. We know that it is somehow linked to memory and we die when we miss enough of it. That covers a lot of what we know about our own sleep.

We know even less about what sleep does for each member of the animal kingdom. We do know that the need for sleep tends to exist in a delicate balancing act with the need to not become some other creature’s midnight snack. Sometimes, that means that animals develop bizarre sleep habits that we find hard to imagine copying.

10 Apes Sleep Like We Do

Every species of great ape sleeps in some kind of bed, whether those are the platforms that wild apes build in trees or the plush mattresses that humans nestle into in the comfort and safety of our own homes.

Lesser apes and monkeys don’t do this, opting instead to sleep sitting on a tree branch while they wobble and sway and occasionally waking up to check for predators. This difference is thought to have been instrumental in the evolution of great apes and, eventually, humans.

As great apes grew bigger, it became harder for them to find branches that could easily and comfortably support them. When the first great ape built a platform to sleep on sometime between 23 to 5 million years ago, the benefits of doing so became apparent.

Those who slept on platforms could shelter higher and were a bit more hidden from predators. At the same time, they were able to rest out of the range of mosquitoes. But the best advantage was that great apes could now get restorative deep sleep which helped enable the improved cognitive functions needed to grow bigger and better brains.^[1]

9 Elephants And Giraffes Sleep Standing Up

As large prey animals, elephants and giraffes are the opposite of great apes when it comes to sleep. They cannot hide away to rest and need to be ready to run at any moment. So they have naturally evolved to sleep standing up.^[2]

Sometimes referred to as a “stay apparatus,” these animals have a knee that locks in place so that they don’t have to rely on their muscles to stay standing in sleep. They share this mechanism with horses, cows, and even birds.

These animals still have to lie down sometimes, though. While standing, they cannot enter into REM sleep. Even though these two creatures require very little REM sleep, they still need it.

An elephant needs REM sleep about once every three to four days and only for about 30 minutes at a time. If they stay on the ground any longer than that, their internal organs may give out under the pressure of their immense weight.

A giraffe sleeps about 30 minutes a day. They tend to get this sleep in very short bursts, usually no longer than five minutes at a time.

8 Dolphins Sleep With One Eye Open

As well as other cetaceans, the dolphin is another creature that can’t exactly lie down to sleep. Most marine mammals have to be on the lookout for predators, but they also have to contend with the fact that they need to consciously breathe oxygen to live.

Unlike humans, dolphins breathe voluntarily and can’t become unconscious without the risk of drowning. Finally, dolphins are warm-blooded mammals living in the cool waters of the ocean. They need to keep moving to keep up their body temperature. When an animal has to keep moving, there’s only one logical thing to do: Just sleep one-half of the brain at a time. Easy.

Unihemispheric slow-wave sleep allows dolphins to get the sort of restorative sleep needed by intelligent animals, but it isn’t just for cetaceans. Many species of birds, especially migratory ones, also engage in unihemispheric sleep.

Unlike migratory birds, dolphins don’t tend to cover large distances while half asleep. Many dolphins manage to hang near the surface or swim slowly, but all generally close one eye to sleep. Probably because of this habit, some have been observed sleeping while swimming in circles.^[3]

7 Newborn Orcas Can’t Sleep

Orcas and other cetaceans don’t sleep for the first month after birth. Usually, adult orcas will sleep about 5–8 hours a day, but neither the mother nor her calf can sleep until 3–4 weeks after birth.

The mortality rate is extremely high for calves, so at least part of this is likely to keep predators away. Not many creatures are willing to contend with a mother orca defending her calf. However, there are a few more reasons that orca calves can’t sleep.^[4]

The calf doesn’t have the muscle strength to keep up with the pod, and it doesn’t have the necessary blubber to stay warm and afloat. To stay alive, the calf needs to stay in its mother’s slipstream where it will be pulled along without getting separated.

As the adult orca must keep moving to generate that slipstream, she can’t sleep, either. Researchers also believe that orca mothers forgo the unihemispheric sleep that cetaceans rely on, too, as none have been observed to swim with an eye closed.

6 Ducks Sleep All In A Row

Unlike orcas, ducks aren’t keen to miss any of their beauty sleep. There’s a reason that to “get one’s ducks in a row” means to have one’s affairs and priorities in order. It turns out that ducks are pretty smart when it comes to catching a few z’s. They can engage in unihemispheric sleep, but they do so using an interesting strategy that wards off any predator looking for a fatty duck dinner.^[5]

Ducks often sleep in a row where the ducks on either side sleep with the outward-facing eye open and one hemisphere of the brain alert. The ducks in the middle get to sleep both hemispheres while secure because of the lookout ducks, and the lookouts get to rest up a little at a time.

All the ducks benefit by getting some sleep without also getting eaten. We’re just hoping that they trade off for lookout duty sometimes.

5 Migratory Birds Power Nap

Scientists have theorized in the past that migratory birds sleep in midair because the only other explanation is that the birds simply do not sleep for weeks or months at a time. Recently, though, Niels Rattenborg from the Max Planck Institute and colleagues from other institutions have studied the sleep habits of frigatebirds. These creatures sleep about 12 hours a day when nesting on land but often spend weeks soaring over the ocean in search of food.

Their study found that the frigatebirds are indeed able to sleep in midair with one or both hemispheres of the brain and can enter into REM sleep without dropping. The birds can do this because they only sleep for a few minutes at a time and only for a few seconds when getting REM sleep. The birds also used their ability to sleep one hemisphere at a time to ensure that they didn’t knock into other birds while ascending and descending.^[6]

4 Reptiles Might Dream

Until recently, the general consensus was that only mammals and birds experienced REM sleep. This is the kind of sleep thought to consolidate memories and the sleep that many creatures risk death to achieve daily. Reptiles, amphibians, insects, and amoebae were excluded from the dreamers.

This was puzzling from an evolutionary standpoint as birds are far more closely related to reptiles than to us. But, with the evidence available at the time, scientists just had to shrug and assume that birds and mammals spontaneously evolved to dream around the same time.

New research from Gilles Laurent from the Max Planck Institute for Brain Research in Frankfurt, Germany, had surprising results that may force us to revise that assumption. When researchers hooked bearded dragons up to an electroencephalogram (EEG), they noticed some very familiar sleep cycles.

The dragons studied went through about 350 80-second cycles per night that seemed simple in comparison to the four or five 90-minute ones that humans experience. Scientists now theorize that mammals, birds, and reptiles share a common ancestor that developed cyclical sleep about 300 million years ago.^[7]

But what do reptiles dream about? Laurent said, “If I were an Australian dragon living in Frankfurt, I’d be dreaming of a warm day in the sun.”

3 Fish Aren’t Afraid Of The Dark

Emmanuel Mignot at Stanford University in Palo Alto, California, and his colleagues performed sleep studies using zebrafish with the hope that they would see whether the fish could suffer from insomnia or sleep deprivation. They found that the fish followed a simple circadian rhythm.

When lights are on, the fish don’t sleep at all. When they’re off, the creatures will nap if there is a sleep debt to pay up. For the fish, it’s far simpler than for mammals. Light triggers the release of a hormone that overrides the need for sleep until nighttime rolls around again. Lucky fish.

This isn’t the case for one particular species of fish, though. The eyeless Mexican cave fish experiences no circadian rhythm whatsoever. Damian Moran of the private company Plant and Food Research studied the eyeless Mexican tetra as well as its surface-dwelling counterpart by putting them both into fish treadmills where they could swim against a current constantly. The surface tetras used more energy under lights than in the dark, while the eyeless tetras didn’t change at all.

It makes sense that a creature that lives in total darkness and is eyeless doesn’t give a flying flip about light cycles, but the most interesting finding was what this meant for their energy use overall. Using less energy at night didn’t leave the surface tetras better off. Instead, they used 27 percent more energy than their eyeless cousins. This energy was spent revving up their metabolisms to expend more daytime energy and slowing it back down at night.^[8]

2 Parrotfish Sleep In A Bubble

Parrotfish are already gunning for a top spot on the world’s strangest animal list considering that they crunch on coral reef and change their color and sex fairly often. But this fish isn’t stopping when it comes to sleeping.

When the parrotfish settles in for a good night’s rest, it activates special glands in the gills to secrete a mucus bubble around itself. Scientists have long debated why the parrotfish does this, postulating that it may lower the chances of being eaten by eels or act as a kind of fishy sunscreen.

Alexandra Grutter from the University of Queensland is one scientist who thinks she knows why parrotfish sleep in a jelly cocoon. Fish who hang around the reef at night are vulnerable to tiny bloodsucking crustaceans called gnathiid isopods. During the day, cleaner fish nip these little ocean mosquitoes before they can latch on. At night, however, even cleaner fish have to sleep.

Grutter tested this theory by removing some sleeping parrotfish from their cocoons and leaving them vulnerable to gnathiids. The exposed fish were attacked mercilessly while the cocooned ones were largely ignored.^[9]

1 Walruses Snooze By The Skin Of Their Teeth

A walrus can forgo sleep for up to 84 hours at a time. While plenty of animals go without much sleep for a long time, only walruses do so regularly and without any notable signs of sleepiness. This finding may force sleep researchers to reevaluate ideas of how much sleep a mammal needs. On land, a walrus can sleep deeply for up to 19 hours at a time, possibly to make up for their sleep debt.^[10]

When not avoiding sleep like a college student cramming for finals, the walrus still acts much like a college kid by sleeping just about anywhere with no problem. When in water, walruses will sleep floating on the surface, lying at the bottom, or standing and leaning. These sleeps are short because a walrus needs to come up for air from time to time.

However, some enterprising walruses have figured out how to have the best of both worlds. They dig their massive tusks into an ice floe and drift off to sleep. Their head stays above water while the rest of their body is submerged, which must be super comfortable for an animal that’s never heard of brain freeze.

Renee Chandler is an Atlanta-based graphic designer and writer. She is currently coauthoring a project that you can preview and support at www.patreon.com/pterohog.

Sleep may not be the highest priority on most people’s to-do lists, often coming second to work or leisure. However, people might need to rethink putting sleep on the back burner. According to experts, individuals above the age of 18 require a minimum of seven hours of sleep to be healthy, and many adults are failing to meet this amount of sleep.

Unfortunately, a recent article reports that “more than 30% of adults have a daily sleep debt—when you sleep less than your body needs—of over an hour, while nearly 1 in 10 adults are missing two or more hours of sleep each night.” Sleep is vital for mental and physical well-being; going without it can have severe side effects. So read along for ten shocking ways sleep deprivation can affect you!

Related: Top 10 Messed Up Things People Have Done While Sleepwalking

10 Poor Sleep Can Make People Less Kind

Altruism, defined as the unselfish devotion to the welfare of others, is vitally important for the well-being of communities. Human kindness is vital for the growth and longevity of communities. However, if sleep deprivation rates continue to rise, generosity may be in short supply in the future. An article from Science News describes a study that analyzed participants’ altruism in relation to their sleep.

The study found that “the more time participants spent awake in bed, a measure of poor sleep, the lower their altruism scores. That drop in altruism held true both when comparing individuals to themselves and when averaging scores across the group.” While this finding may seem trivial, it’s important to remember how human civilizations could thrive based on community and cooperation. Generosity makes the world go round; thus, getting a good night’s sleep will also make the world go round!^[1]

9 Drowsy Driving Can Have the Same Risks as Drunk Driving

Drunk driving is a big no-no, and this is a widely known hazard. However, drowsy driving is an underestimated killer! The National Highway Traffic Safety Administration (NHTSA) estimates that in 2017, “91,000 police-reported crashes involved drowsy drivers. These crashes led to an estimated 50,000 people injured and nearly 800 deaths.” With the uptick in sleep deprivation among those of driving age, the NHTSA has begun efforts to combat drowsy driving. They also provide tips to avoid drowsy driving.

While sleep is the number one way to avoid drowsy driving, it’s also helpful to avoid driving during peak sleepiness periods and make sure to check prescriptions and over-the-counter medications. So, next time you get behind the wheel, make sure you’re free of any drowsiness!^[2]

8 A Lack of Sleep Can Cause Weight Gain & Obesity

Obesity and sleep deprivation are both public health concerns that are growing each year, and they may be closely related. A study published in the National Library of Medicine found that “individuals with short sleep duration (less than 6 hours) were 7.5 times more likely to have a higher body mass index” and that “adults who slept 7.7 hours had the lowest BMI; those with shorter and longer sleep duration had progressively higher BMI.”

Unfortunately, with the correlation between sleep deprivation and obesity, there is also evidence of obesity contributing to sleep deprivation. As stated in the study, obesity can contribute to obstructive sleep apnea, which can cause airways to narrow and can ultimately cause poor sleep. So it’s important to avoid the cycle altogether and get a good night’s rest!^[3]

7 Dementia Risk Can Increase If You’re Not Getting Adequate Sleep

Dementia is a very difficult disease for both the person diagnosed and their loved ones. Symptoms tend to trigger a decline in cognitive abilities and behavior, leading to frayed relationships and poor mental health. Therefore, many individuals are taking precautionary measures to avoid the risk of developing dementia. However, many don’t factor in the role that sleep deprivation may play.

A New York Times article reports that middle-aged individuals who regularly fail to get an adequate night’s rest may be more at risk of developing dementia. The article refers to a study where “compared with those who averaged seven hours of sleep a night, the study participants who slept six hours or less on weeknights were 30 percent more likely to be diagnosed with dementia nearly three decades later.” Therefore, this is an important reminder to prioritize your sleep, as it can help offset other diseases later on!^[4]

6 24 Hours or More Without Sleep Can Cause Hallucinations

Hallucinations are eerie to think about, and for good reason. Hallucinations may look and feel real, but they’re only byproducts of your brain. Thus, if you want to avoid the risk of hallucinations, proper rest is key. A study published in the National Library of Medicine found that after a period of sleep loss, perceptual distortions and hallucinations were “reported in individuals with no history of psychiatric illness” and that “sleep problems correlate with an increased frequency of psychotic disturbances such as hallucinations and delusional beliefs.”

However, don’t stress out too much if you miss a good night’s rest! The hallucinations described were typically observed in extreme cases of sleep deprivation, such as 24 to 48 hours without sleep. But it’s still important to keep in mind that hallucinations are a risk of skipping too much sleep!^[5]

5 Your Heart Can Be at Risk If You’re Deprived of Sleep

Most people know to avoid too much red meat and cholesterol in order to offset the risk of heart attacks, but many individuals are unaware of the impact that sleep can have on the heart. The American Heart Association reports that “people who slept fewer than six hours a night—compared with those who slept six to nine hours—had a 20% higher risk of heart attack.”

With heart disease being the #1 killer of humans for more than 100 years, it’s becoming increasingly important to participate in as many preventative measures as possible to ensure longevity. Therefore, protect your heart by protecting your sleep!^[6]

4 Not Getting Enough Sleep Can Put a Strain on Your Love Life

Having the same sleep schedule as your partner can be amazing! However, if both partners’ sleep schedules fail to provide enough rest, the joint sleep schedules may strain the relationship. Additionally, if one partner is a restless sleeper, it can cause the other partner to struggle to sleep, resulting in both partners getting poor sleep.

A study published in ScienceDirect found that “when both partners slept less, couples interacted in a more hostile way than when at least one partner slept more.” Hostility in relationships can easily lead to partners going their separate ways; however, couples have found a new method to ensure that both parties are well-rested. Couples noticed that they encounter less conflict by sleeping in separate beds or separate rooms. Therefore, if you and your partner struggle to see eye-to-eye on sleep, it might be worth a try!^[7]

3 Failure to Get Proper Rest May Tank Your Productivity

Many people skip sleep to study for a test or finish a task at work. However, this tactic ends up backfiring for many individuals. According to the National Heart, Lung, and Blood Institute (NHLBI), “People who are sleep deficient are less productive at work and school. They take longer to finish tasks, have a slower reaction time, and make more mistakes.”

Additionally, a lack of sleep may even lead to short periods of subconsciously falling asleep, coined as “microsleep.” As stated by the NHLBI, “Microsleep refers to brief moments of sleep that happen when you’re normally awake. You can’t control microsleep, and you might not be aware of it.” So, if you aim to maximize productivity by skipping a few hours of sleep, you might be better off getting a good night’s rest instead!^[8]

2 Your Lack of Sleep May Be Hurting Your Immune System

Your immune system is crucial for fighting off harmful, infectious diseases. However, many factors can weaken the body’s immune system, leading to an increased risk of catching unwanted sicknesses and can even delay recovery. And to no surprise, sleep is one of these factors.

According to the Mayo Clinic, “Studies show that people who don’t get quality sleep or enough sleep are more likely to get sick after being exposed to a virus, such as a common cold virus. Lack of sleep can also affect how fast you recover if you do get sick.” Being sick is never fun—therefore, it’s vital that you get enough sleep to prevent your body from succumbing to illness!^[9]

1 The Benefits of a Good Night’s Rest

With all of the scary side effects of sleep deprivation, it’s important to remember that there are many tactics to help you improve your sleep habits. The National Heart, Lung, and Blood Institute suggests tips such as keeping a consistent sleep schedule, taking an hour before bed for quiet time, and keeping your bedroom quiet, cool, and dark to maximize your sleep. There are endless benefits to getting a good night’s sleep, so make sure to take care of yourself and allow your body to recover properly each night. Sweet dreams!^[10]

For most people, the word “sleep” conjures up peace and relaxation after a long day. However, your body undergoes many changes during the hours that you are unconscious. From undoing the day’s harm to preparing for the day ahead, the human body is constantly sorting, repairing, and refreshing. So next time you wake up feeling like a different person, know that there may be some truth to the thought.

10 Filing Away Memories

Human beings are very active organisms. We do things, go places, and interact with people, all the while creating memories. Memories are stored in the brain. But as anybody who has ever tried to find a file on a crowded desktop knows, saved things are of no use if they cannot be easily accessed and found.

During sleep, the brain actually replays the day’s events, catalogs them, and stores them in the brain’s long-term memory centers. Simultaneously, the brain discards unnecessary memories.

This storing of important long-term memories is critical to humans being able to function properly. This is because long-term memory is essentially limitless and set in stone, meaning that these memories will stay with you for your lifetime.

Most people can remember specific memories from their childhood very vividly but have a much harder time remembering exactly what they did two days ago. This kind of memory prioritization is essential for learning and retaining information as well as developing skills like problem-solving or mastery of a sport or game.

Most of this memory consolidation occurs during one of the deepest parts of sleep, slow-wave sleep, in which there is little other brain activity. As the mind transitions into REM (rapid eye movement) sleep, the brain then stabilizes the critical memories for quick recall later.

9 Blood Pressure And Core Temperature Drop

About 30 minutes before you fall asleep, the body begins to lower its body temperature. This occurs to slow down your metabolism to the point where you can sleep for hours without going hungry. As a result, heart rate and blood pressure also decrease.

While this may not seem like a big deal, your core body temperature drops by more than 1.1 degrees Celsius (2 °F) to around 35.6 degrees Celsius (96 °F), which is one degree above hypothermia. Your body also needs less energy, so you are in no danger of freezing to death while taking a nap.

Upon waking up, blood pressure and heart rate rapidly rise again to keep up with the demand for energy. But for a brief period of time, there is an imbalance, resulting in the sluggishness and clouded thinking experienced by people who have just awakened.

8 Paralysis

Ever had a nightmare and found you couldn’t run or scream? While this can be terrifying, this phenomenon (known as “sleep paralysis”) is what keeps you from acting out all your dreams in real life (which is probably a good thing). During REM sleep in which dreams occur, the brain blocks neurotransmitters and receptors in muscles, effectively paralyzing you.

Occasionally, this can happen briefly when falling asleep or waking up, during which you are fully conscious but unable to move at all. This state is quite terrifying.

It is also the root of many ancient legends, usually involving hallucinations. In these legends, people are visited by demons or other creatures (from the Old Hag in Anglo-Saxon tradition to the “Pinyin” in Chinese folklore) and are unable to move.

7 Stretching

Throughout the day, downward pressure is exerted on the spine due to gravity and your vertebrae compress. As a result, fluid drains out from between your vertebral discs and you actually shrink up to 1 centimeter (0.4 in) by the end of the day. Similarly, when your back is relieved of all that stress at night, the fluid is allowed back into the joint connections, permitting the body to stretch an extra 1 centimeter (0.4 in) or so.

Although this height difference is not that significant, the lack of pressure also enables children and adolescents to grow while sleeping. In fact, we can only grow while asleep. This is because of both the pressure that is taken off the spine and legs when lying down and the growth hormones that are released while sleeping.

6 Sleepwalking

Although not everyone sleepwalks, enough of the general population (around 30 percent) has sleepwalked at least once in their lives to include it on this list. Also called somnambulism, sleepwalking is technically a sleep disorder in which the brain is in a semiconscious state, performing complex tasks such as getting out of bed, going to the kitchen, even driving.

Obviously, this can be very dangerous. But sleepwalking is relatively common, especially among children. Parents, roommates, and friends often report that the somnambulist in question will act dazed and confused while performing bizarre behaviors such as preparing a meal, only to return to bed.

Scientists still are not sure why people sleepwalk, although research has shown that it may be genetic. Sleepwalking usually occurs during slow-wave sleep, in which the brain is busy processing the day’s memories.

This may explain why a sleepwalker’s short-term memory is not very active while in this trancelike state. In fact, the person in question will have no memory whatsoever of the previous night’s events when they wake up in the morning.

5 Body Spasms

When you fall asleep, your body jerks. Every time. As described above, we are usually paralyzed while asleep to protect us from acting out our dreams. However, there is a gray area, a moment when the body is not physically asleep but not awake, either.

This is when most people experience what is called a hypnic jerk. It is believed to be a delay between the brain sending the message to relax and the nervous system getting this message.

We do not fully understand how this reaction came to be. Some scientists suggest that it is left over from a primitive reflex that misinterprets falling asleep to falling out of a tree. Others say that it is just the nerves “misfiring” as they are turned off.

Whatever the cause, hypnic jerks are one of the few reminders of the complex processes that occur while asleep that we can actually observe while awake. This is because a hypnic jerk upon falling asleep can be so violent in some cases that it actually wakes a person back up.

4 Brain Uses More Energy

The majority of energy produced while awake (about 80 percent) is used by various physical activities such as movement, breathing, and speaking. While asleep, this energy is obviously not being used and the “energy surplus” is diverted to the brain.

This means that the brain’s energy consumption is actually higher in certain stages of sleep, such as REM, than it is while awake. This energy is put to good use, completing secretarial tasks that are backlogged while awake, such as creating and strengthening neural connections and removing waste products.

The brain is too busy during the day with more urgent and energy-hungry tasks like decision-making for these other activities to occur. During sleep, however, the brain has some “free time” to tidy up.

3 Lose Weight

Ever wake up to find you are suddenly very thirsty? This is because your body actually loses more than 0.5 kilograms (1 lb) of water to the surrounding air at night.

Think about it this way: The air inside your lungs is hot—about 36.7 degrees Celsius (98 °F). It is also filled with moisture. Since most people’s rooms are much cooler than 36.7 degrees Celsius (98 °F), the air you breathe out as you sleep contracts as it cools, drawing moisture out of the air and your body.

The weight of the lost water is minuscule, only about 0.02 grams per breath. But over the course of the night, this can add up to more than 0.5 kilograms (1 lb) of lost weight.

CO₂ has a similar but lesser effect. Everyone knows that you breathe in oxygen (two atoms) and breathe out carbon dioxide (three atoms). As one more atom is coming out than going in, an infinitesimal amount of mass is lost each time you take a breath.

However, there are about a billion trillion carbon atoms in each breath you exhale, so this adds up to about 0.7 kilograms (1.5 lb) every night. This happens in the day, too, but you more than replace the water and carbon through food and drink.

2 Brain Cleansing

During waking hours, toxins and other waste products accumulate throughout the cells of the brain and body. As the rest of the body shuts down when you go to sleep, your brain gets to work. Essentially, it opens a valve that allows cerebrospinal fluid (pictured above) to flow from your spine into your brain, rinsing the tissue and taking all the toxins with it.

This process is part of a larger cycle known as cellular respiration, a series of reactions that help cells create energy from nutrients and keep the body running. The toxins removed at night are “leftovers” from this process.

Although this cleansing occurs throughout the body, its effects are most noticeable in the brain, where inadequate sleep has noticeable effects. This brain gunk that remains is one of the main reasons you often feel lousy after a long night.

1 Dreams

How could we forget dreams? They are such a mundane but essential part of life, and yet scientists still understand almost nothing about them. This includes the question: Why do we even dream?

If one takes a step back and thinks about it, dreams are quite strange. Every night when your body falls unconscious, your brain conjures up an imaginary reality that exists only in your head but that you think is real. When you wake up, almost all of it disappears from your memory. Despite how strange it sounds, dreams are taken for granted as a fact of life, much like brushing your teeth or going to work.

Although the actual need for dreams remains unclear, the related activities that occur during REM sleep are understood and plentiful: long-term memory strengthening, flushing the brain of toxins, increased “secretarial” work, and so on. This makes it even stranger that we know so little about dreams themselves.

These questions are not anything new. Speculation on the cause and meaning of dreams has been a fixture of human fascination for tens of thousands of years, going at least as far back as the ancient Greeks and Egyptians. Despite the modern technology at our disposal—from MRI scanners to EEG detectors—theories about the origins and purpose of these mysterious experiences will, at least for now, remain theories.

Damian Coburn is an avid reader who also likes to write, travel, and camp.

Next to eating a healthy diet and getting enough exercise, getting adequate sleep is a staple cornerstone to a healthy life. But did you know that sleeping can also be dangerous?

SEE ALSO: Top 10 Amazing Facts About Dreams

There are actually a number of things that can go wrong when you close your eyes and slip into unconsciousness—and for some people, the danger is real enough that they never wake up again. In fact, according to an ancient Greek proverb, death and sleep are brothers . . . death being the perfect fulfillment of sleep and sleep being the imperfect embodiment of death.

Sleep has, for the most part, always been seen as a “passive” activity that our body performs on its own. But the truth is that our brain is actually quite active while we slumber. It’s also true that there are many unanswered mysteries about sleep that modern scientists have yet to unravel.^[1]

As it turns out, there are still some surprising (and somewhat scary) things going on when our conscious brains turn off and our bodies begin the sleeping state. And sometimes, the results can be completely terrifying.

10 Sudden Cardiac Arrest

Sudden cardiac arrest, also known as SCA, can occur when the sinoatrial node, the node in the heart that essentially acts as your body’s natural pacemaker, becomes impaired.^[2] In other words, this condition occurs when the electrical systems of the heart malfunction. And in some cases, it’s deadly within the first few minutes.

How does it kill? Well, it basically reduces blood flow to the brain. And the scariest part? Not only can it happen during sleep, but half of cases show no symptoms before the cardiac arrest occurs.

9 Carbon Monoxide Poisoning

Carbon monoxide, or CO, is a colorless, odorless gas that can be lethal if too much of it enters the lungs. CO can be found in the fumes that come from running cars, stoves, grills, fireplaces, gas ranges, furnaces, and so on, and it can be almost impossible to detect unless a carbon monoxide detector is in use.

How does it kill? Basically, if enough of it builds up in a small enough space, breathing it in can become toxic. And if you inhale enough of it, just having it in your lungs can be enough to “seal the deal” in a very final way. If awake, the victim may experience symptoms like dizziness, weakness, a headache, or an upset stomach.

But what if it catches you while you’re asleep? Well, people who are sleeping often experience no symptoms, and they can die in their sleep.^[3]

8 Myocardial Infarction

A myocardial infarction, more commonly known as a heart attack, can happen during sleep, though thankfully, the odds are pretty good that this specific type of cardiac event will wake its victim up before it kills them.^[4]

Heart attacks happen when blood flow to part of the heart gets blocked. This blockage can destroy part of the heart muscle.

How does it kill? If enough heart tissue gets damaged, the heart may not be strong enough to pump any blood out to the rest of the body. This can result in heart failure, which could be lethal if medical treatment isn’t obtained immediately.

Unfortunately, it usually isn’t possible for a heart attack victim to seek medical attention if they’re asleep—and that’s the part that’s terrifying.

7 Central Sleep Apnea

Central sleep apnea is basically a disorder that causes the sufferer’s breathing to stop and start repeatedly while they are unconscious. It happens when the brain doesn’t send the proper electrical signals to the muscles that control the breathing mechanisms during sleep and is believed to originate from a problem in the brain stem.

How does it kill? Basically, if the case of apnea is bad enough, hypoxemia may set in—which happens when oxygen levels in the body fall below those required for normal life function. This basically leads to oxygen deprivation.^[5]

If the brain is not able to rouse the body in enough time to take a breath, the prognosis can be fatal!

SEE ALSO: Top 10 Surprisingly Common Ways To Die In Your Sleep

6 Unexplained Nocturnal Death Syndrome

This is undoubtedly one of the more “mysterious” inclusions in our list.

Unexplained nocturnal death syndrome (SUNDS) was first reported in 1977 among southeast Asian Hmong refugees in America and Canada. Since then, it has gained a pretty scary reputation in both textbooks and on the dark corners of the internet. In the Philippines, they call it Bangungut, in Hawaii, they call it Dream Disease, and if you’re in Thailand, you call it lai tai, which means “sleep and die.”

The exact cause of death among those who die of SUNDS is actually still unclear, but the presentation always seems to be similar. It basically causes otherwise young, healthy individuals to die in their sleep for seemingly no reason.

How does it kill? Scientists still aren’t sure, but it tends to occur frequently in Southeast Asia, and researchers suspect a range of possible explanations, from malfunctions of the ion channel to ventricular fibrillation.^[6]

5 Cerebral Aneurysm

A cerebral aneurysm, also known as a brain aneurysm, is basically a weak spot in the wall of a blood vessel in the brain. It is kind of like a thin balloon that fills with blood. Over time, as the blood pumps through the artery, it continues to weaken and swell—and if the pressure increases too much, a rupture can occur.

How does it kill? When an aneurysm ruptures, the bleeding usually only lasts for a few seconds. But the blood causes damage to the surrounding brain cells and can increase the pressure inside the skull. If the pressure elevates too much, the condition can quickly turn fatal.^[7]

4 Enterovirus D68

This is one of the more obscure entries on our list, but that makes it no less terrifying.

Enterovirus D68 (EV-D68) is a type of non-polio enterovirus that was first identified in California back in 1962. But back in 2014, there was a huge increase in the number of reported cases, leaving researchers to wonder if the virus was going to become more predominant in coming years than they had expected.

The scary thing about EV-D68 is that while it usually causes mild to severe respiratory illness symptoms, it sometimes produces no symptoms at all. And yet, physicians are saying that the disease has the potential to be more dangerous than Ebola in the US.^[8]

How does it kill? It can cause particularly severe respiratory problems, characterized by a high-pitched wheezing sound that has become a dreaded earmark of infection. It has also been associated with muscle weakness and spinal cord inflammation, which is perhaps even more terrifying than the wheezing.

Dying of an infection is not necessarily common, but sometimes, the symptoms are dangerous enough to kill—even if the victim is asleep.

3 Dry Drowning

Most of us are aware that you can drown in the water—this is obvious, but a lot of people aren’t familiar at all with the term “dry drowning” and what it means. It turns out, it is a pretty horrific way to die!

Basically, the idea behind this danger is that it is a type of drowning that can occur even after the victim has left the water. It’s technically still drowning, but “dry drowning” is the term that has come to be used to describe it, though some doctors have argued for the dropping of said term.

It can occur when inhaled water, even just a drop or two, makes it past the throat and into the lungs. This usually causes symptoms, but they are sometimes mild and easy to miss.^[9]

The scary thing is that this water can cause breathing problems that get worse over time. In some cases, these breathing problems don’t strike until hours, or even days later—after the victim has fallen asleep. So-called “dry drowning” is actually pretty rare when you look at total deaths attributed to drowning, but this makes it no less disturbing.

How does it kill? It basically asphyxiates the victim—depriving them of oxygen until they suffocate.

2 The Widowmaker Heart Attack

While most heart attacks have a decent chance of waking their victims up before death occurs, the “widowmaker” tends to be an exception. We’ve already mentioned heart attacks in general once on this list, but this particular type of infarction deserves its own spot.

Why? Because it’s among the deadliest types of heart attacks that can occur. It happens when the left main artery, also known as the left anterior descending artery, gets blocked. A 100-percent blockage in this artery is almost always fatal without immediate emergency care, hence the nickname.^[10]

How does it kill? Heart attacks with severe enough blockages result in damaged heart muscle. And if the muscle becomes too damaged to pump blood, the result can be fatal.

1 Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a sleep disorder in which the victim repeatedly stops and starts their breathing process during sleep. OSA is by far the most common type of sleep apnea, and as it turns out, it is also probably the most likely reason that a person may die in their sleep.

This type of sleep apnea is literally caused by an obstruction that blocks the airway. This obstruction is usually caused by sagging throat muscles, though the muscles and tissues of the tongue, uvula, tonsils, and soft palate can all play a part. It is estimated that as many as 22 million Americans suffer from sleep apnea but that 80 percent of cases go undiagnosed making it a true “silent killer” that many people remain unaware of.

How does it kill? People with OSA experience sudden drops in blood oxygen levels when they stop breathing. If they’re already at risk for a heart attack, stroke, or heart failure, then OSA can be the trigger that sets a sudden cardiac event into motion.^[11]

In such cases, death may occur before the victim even has a chance to wake up.

Joshua Sigfus is just a writer trying to make the world a better place.

Have you ever woken up to feel an eery presence in your bedroom? Do you believe that you’ve been abducted by aliens or visited by a withered old crone or a humanoid cat figure during the night? Is it normal for you to wake up unable to move, speak, or breathe? If you answered “yes” to any of these questions, you might have experienced sleep paralysis.^[1]

In recent years, sleep paralysis has started to move out of the shadows—no pun intended—and into the forefront of people’s minds. Researchers have now conducted a number of studies into this phenomenon, and the topic has even become the subject of several humorous memes.

But sleep paralysis is no laughing matter. Read on for some truly creepy theories about what happens during sleep paralysis episodes.

Related: 10 Things Sleepwalkers Do (Other Than Walk In Their Sleep)

10 Alien Abductions (American Interpretation)

Roughly four million Americans believe that they have been the subject of an alien abduction. So, it comes as no surprise that many people in the United States and other countries in the Western world believe that sleep paralysis is actually a form of alien abduction.

Many scientists have pointed out the similarities between sleep paralysis and “alien abduction.” And anyone who has experienced a sleep paralysis episode will likely agree.

Sleep paralysis can cause intense visual and auditory hallucinations. A typical experience is to wake up and realize that you can’t move. You may then start to sense a strange presence in the room, and this may be followed by buzzing and humming sounds, bright lights, and a sensation of pressure on your chest or prodding at your limbs.

Sleep paralysis hallucinations can feel extremely real, so many people who experience them wake up truly believing they’ve spent the night on board a spaceship.^[2]

9 Spells of Shamans (Canadian Inuit Folklore)

In Canadian Inuit folklore, the predominant belief is that sleep paralysis results from the spells of shamans. Those spells, they say, prevent human movement and implant in the minds of those affected hallucinations of a formless presence.

In one study, most respondents from this culture recognized sleep paralysis as either “uqumangirniq” or “aqtuqsinniq.” Those who believed in the state of uqumangirniq said that people’s souls were more “vulnerable” during sleep. During this period of vulnerability, they say, shamans or malevolent spirits are more able to attack the soul, thereby causing sleep paralysis.

The researchers noted that the respondents’ perception of sleep paralysis as an experience of “supernatural power” reinforced their belief in the spirit world. But is that belief what invited such malevolence into their lives in the first place?^[3]

8 Paralysis Magic (Japanese Folklore)

In Japan, sleep paralysis is known as “kanashibari.” This word derives from the name of a medieval Japanese spell known as “kanashibari no ho.”

Broken down into its literal Japanese meaning, kana means metal, and shibari means to bind: “to immobilize as if bound with metal chains.” (Remember, when people wake up in a sleep paralysis episode, the first thing they often become aware of is that they are unable to move.)

The spell kanashibari no ho was a form of paralysis magic, which priests of Onmyodo Shugendo are said to be able to attain with extreme self-discipline and by refraining from all forms of indulgence.

According to some texts, those who were able to practice this paralysis magic often used the kanashibari no ho spell to remove evil spirits. This is somewhat ironic, though, given that many people who experience sleep paralysis are often met with what they consider to be evil spirits…^[4]

7 Pisadeira (Brazilian Folklore)

Though many sleep paralysis sufferers are faced with shapeless forms and nameless entities, in some cultures, the entity that invades so many people’s dreams has a name. And in Brazil, it is known as the Pisadeira. In Portuguese, this term translates to “she who steps.”

Many pieces of literature on the topic describe the Pisadeira as a crone. True to the Portuguese translation of her name, this crone is said to lurk on people’s roofs during the night. And when she finds a sleeper who has gone to bed on their back and on a full stomach, she enters their room and stamps on their chest.

This is interesting for a couple of reasons, the first being that sleep paralysis usually causes sleepers to experience a feeling of compression in the chest area. Another reason is that sleep paralysis most often affects those who sleep in the supine position or on their backs. Could there actually be some weight behind this belief?^[5]

6 The Old Hag (Newfoundland Folklore)

“The Old Hag” is another common name for the sleep paralysis demon, and this term for the phenomenon is thought to have originated in Newfoundland.

Like the Pisadeira, the Old Hag is a crone-like old woman who sets out to make sure that sleepers are unable to breathe, move, or call for help by sitting heavily on their chest in the night.

The origin of this belief can be traced back to the 1890s when the Journal of American Folklore published a short article about the phenomenon. And to this day, locals are still careful never to sleep on their backs. Because if they do, it leaves them unprotected from the Old Hag, who uses the cover of the night’s darkness to invade the bedrooms of so many innocent sleepers.

Scientists say that the experience is down to brain activity (more on this later), but for many Newfoundlanders, the horrors of being visited by the Old Hag are all too real for them to believe that it is all in their head.^[6]

5 A “Glitch” During REM Sleep

Scientists in much of the Western world have attempted to dispel many of the folkloric beliefs on this list by presenting us with a much less outlandish explanation for the horrors of sleep paralysis: an imbalance of neurochemicals in the brain.

During random eye movement (REM) sleep, the brain releases chemicals to paralyze the body and prevent people from acting out their dreams and harming themselves in the process. But sometimes, a glitch in this process means that the brain is able to wake a person up while their body remains stuck in paralysis mode.

At this point, a person becomes conscious, but the dreams they were having while in REM sleep continue to play out. And instead of taking place inside their head, those dreams are now taking place before their very eyes…and they are not usually pleasant ones.^[7]

4 Possession

As if a crone invading your room in the dead of night wasn’t creepy enough, imagine having a demonic entity invade your mind, body, and soul. This is what happens in possession, and sleep paralysis experiences have been linked to possession for centuries.

During the Christian era, the friends, relatives, and neighbors—not to mention the local religious leaders—would pray for the souls of those who experienced this apparent possession. Exorcism, during which malevolent spirits are forcibly evicted from the body believed to be possessed, might also have taken place.

This is without doubt one of the most disturbing sleep paralysis theories out there; we can usually wake from a slumber, but possession leaves us absolutely powerless.^[8]

3 The Jinn (Egyptian Folklore)

If you’ve ever seen Aladdin, you’ll know that the genie is a loveable character who will do anything he can to help the eponymous hero in his quest to marry Princess Jasmine. But according to Egyptian folklore, genies aren’t always so generous.

The term “genie” is the anglicized version of the word “jinn.” And in Egypt, the Jinn is said to be a spirit-like entity that “torments” people when their bodies are in the state of paralysis that REM sleep causes.

But the Jinn doesn’t only haunt people in their dreams. So intense is the fear of this character among Egyptians that they may actually be more likely to wake up in the middle of REM sleep. And conversely, as we already know, this only invites evil in…^[9]

2 “The Ghost That Pushes You Down” (Cambodian Folklore)

We’ve covered genies, hags, crones, demonic entities, and magic in this list, but we haven’t yet touched on possibly the most common paranormal trope: ghosts.

Cambodians and other Southeast Asian cultures widely believe that their sleep paralysis episodes are the results of visitations from ghosts. But not any old ghosts…specifically, “ghosts that push you down.”

According to some literature, this belief has its roots in the conviction that people experience sleep paralysis, not because of poor health or a “glitch” in the brain, but due to how lucky (or, let’s face it, unlucky) they are.

This piece of folklore shares a common theme with many other cultural beliefs covered on this list: that there is a sense of being pushed down, pinned to the bed, or trampled on during sleep paralysis. Science seems to explain why we hallucinate and cannot move, but what explanation does it have for this?^[10]

1 Pandafeche Attack (Italian Folklore)

In some regions of Italy, notably Marche and Abruzzo, people characterize sleep paralysis as an attack by the Pandafeche.

Reports given in studies suggest that the Pandafeche can take multiple different forms, each as terrifying as the last. Some people report seeing a witch or a crone, while others say their night-time visitors remind them more of ghosts or spirits. Oddly, some Italian sleep paralysis sufferers explain that the Pandafeche presents to them as a frightening cat-like entity.

Although descriptions of the Pandafeche figure seem to vary, people seem to agree that the only way to prevent an attack by this horrifying creature is to leave a pile or a bag of sand somewhere near the sleeper’s bed. The theory goes that the Pandafeche will always stop to count how many grains of sand are present and thus delay their attack.

This raises an interesting question: Are there any other forms of distraction that could help ward off the evil that seeps in when sleep paralysis strikes? If so, let’s hope we find them—and soon. After all, nobody wants to wake up face to face with a demon, do they?^[11]

Human sleep is a relief to the weary, while sometimes despised by the hard driven. Essential and mundane, human sleep is still mysterious, enticing determine researchers with its enigmas. And when affected by physical or psychological disorders just as any aspect of human existence may be, sleep is often anything but restful, bringing disturbance and sometimes, disaster. In this list, we explore the most startling facts about sleep and learn what happens when slumber goes dramatically wrong.

10. Fatal Familial Insomnia

Insomnia might seem to be a garden variety annoyance, and indeed it is only that in the vast majority of cases. However, a far more dangerous kind of inherited insomnia than the mundane version experienced by the stressed or overexcited can lead to death over a period of worsening bouts. Caused by a hereditary prion condition that targets the thalamus, the part of the brain responsible for controlling the sleep/wake cycle, Fatal Familial Insomnia brings an inorexible cessation of sleeping ability. The disorder usually activates between ages 32 and 62, causing death within 12 to 18 months. Unable to gain any meaningful sleep, sufferers die as a result of both neurological degeneration and increasing, extreme sleep deprivation.

Prions, made infamous by “Mad Cow Disease” are bizarre protein agents that kill by converting healthy proteins in an infected organism into a similar folded form, destroying their function. The effect is somewhat analogous to the takeover of a human body by a virus, bacteria or cancerous condition, but completely unique in nature. In the case of Fatal Familial Insomnia, a genetic mutation triggers the prion forming process and the damage to nerve cells that defines the disease. Fortunately the disease, for which there is no cure, is extremely rare, affecting only a handful of families worldwide. In a couple where one member carries the mutation for Fatal Familial Insomnia, there is a 50 percent chance of passing the genetically dominant disorder onto their children. In rare cases, the disorder may occur spontaneously, when proteins in a person’s body shift into the disease forming structure due to unknown causes.

9. Sudden Unexplained Nocturnal Death Syndrome

A rare and by default always fatal condition most frequently reported from Southeast Asia, Sudden Unexplained Nocturnal Death Syndrome (SUNDS) has disproportionately affected those of Southeast Asian backgrounds and led to intense scientific investigation. Initially described in 1917, the condition causes victims, generally young men in apparently OK health and no serious medical history, to die suddenly in their sleep, with deaths being the most frequent in the early morning hours. Primarily affecting defined genetic groups in different parts of Asia, SUNDS affects different groups to varying degrees, with much higher levels among certain populations from Thailand and the Philippines as an example, with far lower rates of occurrence in Southern China.

The condition rose to prominence in the United States as significant numbers of refugees fleeing conflict in Southeast Asia came to the United States and gained notoriety by causing frequent, mysterious deaths through sudden nocturnal heart failure. Stress related causes, shock and cardiac conditions have all been posited, with research from Oxford suggesting heart failure through ventricular fibrillation brought about by genetic mutation based abnormalities affecting sodium channel currents. At night, the heart beats in a weaker pattern, according to Matteo Vatta, Baylor College of Medicine in Houston, making the victims of the disease. The ability of the condition to cause sudden death at night inspired the 1984 movie A Nightmare on Elm Street and has a number of traditional names in different Asian cultures reflecting awareness of the deadly condition.

8. Hypnic Jerks

While restless leg syndrome is well known, less frequently described but more often experience is a sensation of literally falling while falling asleep. Technically not a sleep disorder but simply a sometimes unsettling occurrence affecting sleep, the phenomenon known as Hypnic Jerks is strange and the cause of some disturbing or even traumatic experiences while asleep and may lead to a loss of rest. The occurrence reflects a complex physiological conflict between the motor system and the paralysis that our body goes into when we sleep in a transition between the two states of sleeping and being awake.

As we fall into sleep, the reticular activating system that controls wakeful activity surrenders to the control of the ventrolateral preoptic nucleus, which puts us into a sleep state. When the ability of the sleep state to take over is impaired, Hypnic Jerks occur more commonly and prominently. Under stress, the conflict is more apparent as our ability to fall asleep is impaired, causing the waking state to have an “unfair advantage” over the action of the ventrolateral preoptic nucleus, creating a greater struggle in the form of more Hypnic Jerks. Hypnic Jerks reflect how the stress that makes the process of falling asleep more difficult can cause further disruptions through the jerking action right when one is finally about to fall asleep, further delaying entry into REM deep sleep.

7. Sleep Driving

We all should know the dangers of driving while drowsy, but a bizarre form of “complex automatic behavior” as it is known in the medical field has become of inquiry into the safety of anti-insomnia medication, bringing a host of legal issues. Sufferers of sleep driving episodes have been arrested in various states of consciousness while operating their vehicles. Following such perplexing, potentially fatal and legally problematic incidents, survivors of sleep driving have been noted to suffer amnesia, having no recollection of the incidents.

In certain cases, those affected by this automatism condition have been found in their vehicles clothed fully in bedroom wear or stopped at green lights in their vehicles. Legal cases have led to discourse highlighting a lack of awareness among some physicians and other clinical practitioners of the fact that use of the hypnotic sedative Zolpidem may cause complex automatic behavior in the form of driving while in a sleep state. Although complex behaviors and sleep driving after Zolpidem ingestion have been described, the timing of the ingestion and the legal ramifications of the behaviors are not commonly appreciated by the clinician. The most popular sleeping pill known to be used in the United States, Zolpidem may deserve closer scrutiny by medical professionals to reduce the risk of tragedy by driving while asleep.

6. Obstructive Sleep Apnea

https://www.youtube.com/watch?v=yloiMLsUaU0

Snoring may seem to be the greatest possible annoyance when sleeping in close quarters with other human beings. Yet, snoring can also be a sign of a potentially life shortening condition called Obstructive Sleep Apnea (OSA) where repeated closure of the airway create cycles of oxygen deprivation and complete breathing cessation, waking, a return to sleep, and another breathing interruption and waking. With hundreds of cycles occurring per night, the oxygen deprivation resulting from attacks of Obstructive Sleep can be substantial.

Adequate oxygen is a key factor in circulatory health, and without it, the heart suffers as it runs less efficiently and under greater strain that impacts the entire body negatively. places great strain on the cardiovascular system. The condition thus brings an increased risk of high blood pressure and heart conditions including heart attack, stroke, heart failure, and arrhythmia. Increased risk factors for development of Obstructive Sleep Apnea do not only include innate physiological features. Along with collapse of soft tissue located at the rear of the throat, obesity with excess fatty tissue in the throat area increases the chance of developing OSA by obstructing breathing and causing bouts of OSA. Attempting a reduction in unnecessary body fat and sleeping in alternative positions are among the options available to potentially mitigate OSA’s harmful effects.

5. Sleeping Beauty Syndrome

Kleine-Levin Syndrome (KLS), popularly known as Sleeping Beauty Syndrome, is a peculiar sleep disorder that actually affects young people, especially males, in the majority of cases despite its name. Persisting for several years after onset in most cases, the exceptionally rare but life-disrupting disorder involves sleeping like a cat, in fact more than a cat would. Coming in recurring episodes that may last multiple weeks or even for months, KLS sufferers suffer greatly extended sleeping hours, sleeping for most of the hours of a given day, at times only getting up to eliminate.

The disorder usually disappears as one progresses a little further into adulthood, but may last as long as 10 years after onset. Strangely, the apparently drugged state in which the afflicted find themselves may bring on a suite of bizarre behaviors and predilections, including childlike talking, naivety, and a spaced out, disoriented demeanor. The disorder is severe to the point where those afflicted cannot care for themselves, yet sufferers are apparently normal in between the attacks. The disorder can lead to serious harm to social, personal and academic performance, and may also be accompanied by binge eating and confusion between real life and dreaming.

4. Exploding Head Syndrome

While the name Exploding Head Syndrome makes this disorder sound as if it is the worst of all sleep disorders, Exploding Head Syndrome is more of a disturbing and perplexing phenomenon than a directly harmful condition. However, the disorder may cause an appreciable level of distress as it is defined by the perception of loud noises in the process of falling asleep or waking up. Sounds heard may resemble doors slamming, static or metallic clashes. In certain cases, the anxiety produced from attacks may be enough to bring about heart palpitations and tachycardia.

Perplexing to medical scientists, various physiological causes have been proposed as mechanisms causing the symptoms of Exploding Head Syndrome. Mild seizure activity, neuron related challenges affecting the brainstem and even ear component problems have been put forward as potential triggers of Exploding Head Syndrome.  The condition is correlated to an extent with stress and exhaustion, and occurs most commonly after 50 years of age with slightly more woman than men affected. As a patient falls asleep, the sound may be triggered, only to disappear upon awakening. When the patient tries again to fall asleep, symptoms may return, further inhibiting sleep. The occurrence of the attacks is not predictable, ranging from single episodes to frequent or occasional repeat bouts.

3. Nocturnal Hyperhidrosis

The idea of drowning in your sleep may seem like an unpleasant joke, but the worst instances of night sweats make the idea plausible to sufferers. Known technically as Nocturnal Hyperhidrosis, extreme nighttime sweating may leave sleepwear and bed sheets literally soaking wet as water is released from the body in massive quantities. Often used as a trope in horror movies, awakening drenched in sweat has a variety of medical causes, some minor and some life threatening. Frequently seen as a result of menopause, Nocturnal Hypohidrosis is not related to the temperature of the sleeping environment, but may result from disease conditions as diverse and serious as cancer, bone infections, sleep apnea, diabetes and intestinal disorders, as well as severe anxiety and stress.

Nocturnal hyperhidrosis is capable of causing great physical discomfort and may lead to becoming those affected feeling chilled as the waterlogging, copious quantities of perspiration begin to evaporate. The condition may indicate some of the most serious diseases known, including bone cancer, heart disease, lymphoma, and in some circumstances, serious psychiatric conditions requiring intervention. The International Hyperhydrosis Society notes the importance of seeking a medical evaluation in cases of Nocturnal Hyperhydrosis given the potentially health impairing or life threatening medical conditions the symptoms may indicate.

2. Catathrenia

Catathrenia is a strange name, and even stranger is the nature of this sleep disorder. Categorized as a parasomnia until 2013, when it was re-classified as a breathing disorder by the International Classification of Sleep disorders manual ICSD-3. Sufferers of Catathrenia, which is also known by the name of Nocturnal Groaning, make peculiar sounds while sleeping that range from groans to shrieks. The sounds result when sleepers hold and then release their breath following a deep inhalation, most frequently during REM sleep.

The condition is essentially opposite to the situation that defines snoring, where sounds are made as a person inhales in an aberrant manner. Unlike many other sleep disorders, Catathrenia frequently fails to awaken those it affects. As a result, those experiencing the condition may not be aware of their condition. Lasting up to 30 seconds, the groaning sounds often wake up others sharing a sleep environment with the sufferer. Strangely, those with Catathrenia do not have any distress showing in their facial expressions despite the volume and length of the sounds made during sleep. The condition does not appear to be serious compared to other sleep disorders but may result in a sore throat in the hours following awakening.

1. Nocturia

Bedwetting is a commonly known affliction, yet another disorder involving liquid waste is perhaps more disruptive to sleep though it does not generally result in a wet bed. Nocturia, or Nocturnal Polyuria as it is also called may force a sufferer to rise from their sleep up to six times in a single night to urinate before trying to catch a brief rest in between episodes. Once incorrectly thought to result from bladder fullness, Nocturia is in fact frequently attributable to a failure in the body’s natural urine volume reduction system that would normally activate as we sleep, keeping us dry and well rested.

Typically, the human body automatically concentrates urine produced during sleep through diurnal excretion of solutes such as electrolytes, while the anti-diuretic hormone vasopressin is released at night to suppress urination. Thus, less urine is produced and the natural tendency to release it is inhibited. This biochemical functioning works well to prevent disturbance of sleep by the repeated need to eliminate fluid, but sufferers of Nocturia enjoy no such benefit and face serious sleep disruptions and deprivation as a result of constant trips to the bathroom in the most severe cases. Even a couple of trips to the washroom may cause tiredness in the daytime. Fortunately, the worst and most disruptive cases of Nocturia are quite uncommon.  

You may not believe this, but sleeping is a very controversial topic. People are torn between what the doctors say about an average of 8 hours a night and celebrities like Steve Harvey saying if you sleep 8 hours a day, you will never be successful in life.

No matter where you fall on the sleep debate, there are some actual benefits to getting enough sleep. Your immune system gets a boost; it improves your mental capacity, reduces stress, and helps to improve your mood. The rich and the famous have their own ways of trying to hack sleep to make it work better for them. Here are 10 bizarre sleep habits of the rich.

10 Michael Phelps Sleeps in an Elevation Chamber

Estimated Net Worth—$80 million

Why They Are Rich and Famous