Throughout the ages, humans have sought different ways to change their perceptions and alter their states of being. Many ordinary people, spiritual gurus, monks, and even priests have relied on shifting their conscious experience to achieve some sort of enlightenment or even simple joy.

Euphoria, confusion, and delirium have all inspired and transformed people. Many methods to achieve these ends come with a truly phenomenal experience: hallucinations. One Swiss scientist defined hallucinations as “perceptions without the corresponding stimuli.”

Hallucinations can be terrifying, especially if you’re not expecting them to happen. But for some individuals, they’re downright fun. Here are 10 different types of hallucinations that humans experience and what they’re all about.

10 Excitation

Yes, something as simple as excitation can cause hallucinations and often does. The state of the brain which influences the mind and all its perceptions is a paramount consideration when it comes to the nature and origin of hallucinations, which can often result as a break from the homeostasis of the resting, so-called normal state of brain functioning.

In some people, things like anxiety can trigger hallucinations and the psychosis that sometimes ensues. Anxiety is not experienced in a calm state of mind. It’s directly caused by an overstimulation of the brain, much like what happens when people ingest certain drugs.

Hallucinations through excitation and anxiety aren’t necessarily signs or symptoms of an underlying mental illness. They’re simply a physiological response to the stress (or perceived stress) that the brain is experiencing.

These states of mind and the hallucinations—the vivid, terrifying light, the loud noises which didn’t really happen, the chatter which sounds like voices in the wind—all of this can happen to sane, ordinary people under the right conditions. So if you experience anxiety or excitation that causes hallucinations, you’re not alone. A lot of people share this experience.^[1]

9 Sleep Deprivation

Sleep deprivation is something that college students often experience religiously, and religious people often use it as a means of studying spirituality. But in all cases, under the right conditions, you might just end up with hallucinations.

Most of us have experienced this—the tiny, dancing movements that you know aren’t real, that feel so real, and that are just outside your focus. By and large, the mind comes from the brain as the various centers of the brain process their respective portions of our consciousness, which form a cohesive experience.

That said, if one goes for long periods of time without sleep, these centers of the brain and their constituent neurons begin to degrade, which eventually causes an inability for the brain as a whole to create a unified experience of consciousness. Thus, it is unable to make reasonable sense of the stimuli from the outside world.

Sleep deprivation mainly targets the visual cortex, and approximately 80 percent of people experience visual hallucinations when they don’t get enough sleep. Auditory hallucinations don’t occur with sleep deprivation.^[2]

Not all of this is under our control as it’s more than just staying up late watching TV. A slew of conditions, such as snoring, can prevent someone from getting enough sleep and send him down a path to hallucination. Sometimes, it’s just minor things that you see out of the corner of your eyes. But for some people, the hallucinations become bizarre, extreme, seemingly very real, and even nightmarish.

8 Hypnagogic Hallucinations

Hypnagogic hallucinations are the next most common type of hallucination caused by things relating to sleep. Experienced by 37 percent of the population, this is something we grow out of with age for the most part.

Have you ever been falling asleep and right before you get to the point of no return where you swim into your own little dreamland, you awaken suddenly, partially suspended in a purgatory between waking life and dream life? When this happens, many people experience hallucinations involving their waking selves and seemingly their dream at the same time. This is a hypnagogic hallucination.

Even more terrifying, these sorts of sleep hallucinations are primarily auditory in nature. They include ringing sounds, unpleasant or uncomfortable noises, chatter or popping, and even voices talking to you.

If people use certain drugs, even when they’re not on the drug itself, they can often experience hypnagogic hallucinations in the form of beginning to fall asleep, being suddenly jolted awake, and then suspended in a distorted reality of waking life. They perceive bugs or insects crawling all over their bodies, which sometimes causes these individuals to itch, scratch, or otherwise remove the hallucinatory objects from themselves.^[3]

7 Hypnopompic Hallucinations

The hypnopompic state occurs between waking up from sleep and being fully awake, and many know all too well that hallucinations can occur then, too. However, hypnopompic hallucinations are much less common, only experienced by approximately 12.5 percent of the population.

One of the common themes is sleep paralysis. It is a terrifying experience where the body is wholly paralyzed, suspended between wakefulness and sleep, and some rather dark sensations, even hallucinations, occur.

Sleep paralysis can be either hypnopompic or hypnagogic, but the feelings and fear are always the same. When transitioning out of sleep, the person senses some evil force coming toward him or in the room with him. Often, people report being stepped on, punched, or otherwise attacked by this entity—all while they can’t move.^[4]

Many creatures, demons, and ghosts have been attributed to this supposed entity. It’s seemingly universal and has been around and discussed since at least the days of ancient Greece, whose residents attributed the terrifying hallucinations to succubi and such.

Thanks to science, we now know that these terrifying hypnopompic hallucinations are actually errors in the brain that happen when there’s a problem with REM sleep. It’s a natural, albeit uncomfortable, part of how the brain works.

6 Blindness

One of the most fascinating forms of hallucination are the intense visual hallucinations of the blind. It’s actually rather common for blind people to see things that aren’t there or that they wouldn’t be capable of seeing.

These natural, nonpsychotic “trips” are precise, clear, and often elaborate. The experiencer is usually perfectly sane while seeing 140 small white gnomes prancing around in the snow in synchronization. Many people consider the hallucinations nothing shy of sublime, while others find them terrifying.

Charles Bonnet syndrome is the official name for this. Although the term was coined in the late 1700s, this phenomenon was nothing new. However, few know about it. One 64-year-old blind patient saw snakes crawling into and out of her body. Talk about a wild experience.

It’s estimated that at least 20–30 percent of the visually impaired population have these hallucinations. For obvious reasons, many people don’t feel quite right reporting them to others, including friends or family, for fear of mockery. So that number may be much higher.^[5]

5 Sensory Deprivation

One of the most challenging, terrifying, and unusual experiences is sensory deprivation. The brain was designed for all the senses to take in just the right stimuli to keep the organism alive. It was not intended to be deprived of these things.

This happens because the brain tries to adjust to the new level of sensory input, which is far different than normal. Any incremental changes are experienced as unusual and new phenomena.

This corresponds to hallucinations from excitation, where the brain is starved for new sensations but their input has been strongly blunted. It is much like a starved person who doesn’t need a full meal to be satisfied as he readjusts to a life with food again.

When the brain receives no sensory input for sound for long enough, it eventually begins to invent things from whatever hints of sound it supposes are there. People end up hearing imaginary voices and full-on conversations inside their heads.

This coincides with both the visual hallucinations of the blind and phantom limb syndrome, in which an amputee experiences sensations in a part of the body which is gone. The brain doesn’t receive the input it’s used to, so it just makes up whatever it thinks might be there.^[6]

4 Schizophrenia

One of the tragic hallmarks of schizophrenia is vivid hallucinations. These often present in the form of annoyances–such as hums, buzzes, and noises—for the person suffering from the affliction. Imagine having a hummingbird or an insect flying right next to your ear for several hours.

The visual hallucinations are much like the static of an old TV set displayed over the person’s field of vision. It’s like seeing the world through the craziest photo-video filter you can think of. Schizophrenia is a disease which gives people all sorts of hallucinations, not just those auditory ones mentioned already, but tactile, visual hallucinations where they close their eyes and “sense” themselves in other worlds.^[7]

Hearing voices or sometimes seeing and hearing people who aren’t in the room are common experiences in those diagnosed with schizophrenia. Having people whom these patients trust to tell them what is actually going on in the outside world is absolutely vital for many people with this disease.

With a nearly constant state of mind that misinterprets the inputs that the brain is receiving, it’s no wonder that this terrifying disease leads down the path of delusional thinking and behaviors. How do you know what’s real if all your sensations are lying to you at least a little bit?

3 Trance States

When humans didn’t have access to powerful drugs, they relied on a simpler and much more personal way of achieving the desired hallucinations through trance states and self-hypnosis. We’ve all heard that drugs such as dimethyltryptamine (DMT) can transport someone out of his body into what’s seemingly another world. But did you know that we can do this simply with the power of our minds?

This process is called autoscopic hallucination. The person transcends his body and experiences another world which is totally in his mind. For a few seconds or possibly minutes, a person is “out of his body” like a short, strong drug trip or near-death experience.

Autoscopic hallucinations can come from the trance states inspired by deep meditation and other means by which people transcend reality using nothing more than their mental faculties. Believe it or not, self-hypnosis is a very real thing. It can be achieved through concentrating on a single focal point, using the power of the mind to eliminate your surroundings, and replacing them with something totally hallucinated.^[8]

This may be the oldest form of intentional hallucination, perhaps besides mushrooms or other substances which can bring about such states. But don’t underestimate the power of the mind to intentionally conjure up hallucinations.

2 Epilepsy

Different types of epilepsy can cause different types of seizures and experiences in the affected individuals. Sadly, much like those with paranoid schizophrenia, epilepsy sufferers can have hallucinations accompanied by a fear of persecution or a feeling that someone is out to get them for some time before the onset of a seizure.

It is now being discovered that epilepsy can also cause powerful auditory hallucinations. This happens when the left temporal lobe is damaged. We’re not talking about the fuzz or chatter of other types of hallucinations but extremely complex strings of sound heard by the afflicted person.

We’re slowly starting to piece together the entire story of how epilepsy affects the brain, but it is known that some people experience extremely powerful hallucinations and sometimes a feeling of transcendence. About 80 percent of seizures in those with temporal lobe epilepsy are focal aware, otherwise known as aura seizures.

Although the patient is conscious during the whole seizure, he hallucinates the entire time. This type of seizure only affects one portion of the brain and can produce vivid, astonishing hallucinations.^[9]

1 Drugs

Probably the best-known form of hallucinatory experience in most places is the use of drugs or other mind-altering substances. From LSD to psilocybin, the way that chemicals affect the brain to cause hallucinations has often been described as “jamming the circuits.”^[10]

The transmission of information, usually by way of chemical compounds in the nervous system, creates an excessive stimulation of the senses, at least perceptively. Drugs are the synthetic way to produce sensory overload, and things become transposed and blurred. Anyone who’s taken these drugs will know exactly what I’m talking about.

A lot of science backs the idea that these sorts of chemically induced states are actually quite good for your physical and psychological health. Other hallucinations happen when people intentionally or accidentally poison themselves with certain plants.

These methods have been practiced by humans to achieve hallucinatory experiences for thousands of years. Some of these plants were considered to be medicinal by ancient and tribal cultures. Now science may be confirming their beliefs.

I like to write about the weird, the dark, odd, and unusual. Here’s a fun little piece on different types of hallucinations.

Although people sometimes think of “art” as only or primarily the visual arts, fine arts are much more varied. According to The Dictionary of Cultural Literacy, they include not only painting and drawing but also “sculpture, literature, architecture, drama, music, dance, opera, and television and movies.”

It is in this broad sense of the meaning of the term that the artists on this list are included. Each of them, whether a painter, a novelist, or a poet, is not only famous but also shares the rather surprising experience of having had one or more of their works inspired by a hallucination.

Related: Top 10 Frightening Facts About Hallucinations

10 Futuristic Images

Dr. Jean Kim believes Yayoi Kusama’s art teaches us how to live. The Japanese painter’s work features polka dots, the trademark theme she developed when she was 10 years old, and incorporates imagery from the hallucinations that the artist experiences.

Kim describes Kusama’s art as a mixture of abstract expressionism and conceptual art characterized by its graphic, colorful, and somewhat futuristic images. Kim cites the artist’s Infinity Rooms as an example: “These rooms are small self-contained mirror chambers, allowing the viewer to simultaneously lose one’s identity and sense of self in the infinity of a repeated image evoking the universe.” She adds the paintings capture the reality of selfies, which have become increasingly popular in recent years, as they’ve been distributed rapidly far and wide via social media.

Kusama’s art also helps the artist herself cope with, and even transcend, her mental illness. Kim points out that although not specifically diagnosed, it is consistent with psychosis and possible schizophrenia. While marked by hallucinations and “the disintegration of one’s sense of self and identity, leading to anxiety and paranoia.” Kusama’s art is therapeutic, allowing the painter to reconsolidate the fear of disintegration that the artist experiences.^[1]

9 Stalking Crustaceans and Bizarre Transformations

In 1935, French existential philosopher, novelist, and playwright Jean-Paul Sartre (1905-1980) decided to take a trip—a very special kind of trip. He prevailed upon his friend, Daniel Lagache, a medical doctor, to punch his ticket, so to speak, by injecting his patient with mescaline, which was used at the time to treat alcoholism and depression.

As a result, Sartre experienced a “bad trip.” Writer Emily Zarevich describes some of the more salient features of Sartre’s mind-blowing adventure. Not only did bizarre, frightening crustaceans pursue him wherever he went, but ordinary objects transformed themselves into animals, “his clock [becoming] an owl, his umbrella to a vulture.”

Sartre’s adventure ended with a mental breakdown. Part of his campaign of redemption that followed included his consultation with famed psychoanalyst Jacques Lacan. After that, Sartre understood that the crabs that had pursued him symbolized the philosopher’s fear of being alone. Although he was able to rid himself, intermittently, of the crustaceans that haunted him, the crabs reappeared in Sartre’s experimental and ground-breaking 1938 novel La Nausée (Nausea). In the book, readers are treated to a ludicrous sex scene in which the main character daydreams he’s trapped in a garden full of insects and animals walking crab-style.^[2]

8 Shapes on the Ceiling

Despite his eventual fame, Joan Miro (1893-1983) was once a starving artist. The surrealist painter himself explained the way that he conceived the subjects of his art. Janis Mink summarizes his process in her book, Miro. Upon returning to his Paris studio at night, he would go to bed sometimes without supper, where he would see things, including shapes on the ceiling, before jotting them down in a notebook. Sometimes, the sights were “remembered dreams” from his unrestful sleep; other times, they were images seen in “hallucinations caused by hunger.”

Although Miro might appear to have sufficient funds for necessities and “trips back and forth to Spain,” he was actually impoverished. His hunger, though, like the “ether, cocaine, alcohol, morphine, or sex” that his colleagues employed, helped him to get in touch with his subconscious. This worked out well for Miro, who was too deeply spiritual to destroy his own body and fully enjoyed his own connection to nature. His 1925 painting, The Birth of the World, quickly attained fame.^[3]

7 Blood Sky and Open Chest Wound

Edvard Munch (1863-1944), who, according to Dr. Albert Rothenberg, may have had bipolar disorder with psychosis, experienced visual and auditory hallucinations and received psychiatric hospitalization in 1908.

Munch himself explains the origin of his celebrated, if dark and disturbing, painting The Scream (1893): “I was walking along the road with two of my friends. Then the sun set. The sky suddenly turned into blood, and I felt something akin to a touch of melancholy. I stood still, leaned against the railing, dead tired. Above the blue black fjord and city hung clouds of dripping, rippling blood. My friends went on again. I stood, frightened, with an open wound in my breast. A great scream pierced through nature.”

The experience, clearly a visual hallucination, was creatively transformed by Munch in several phases over a period of eighteen months into a work of art. Five preliminary sketches in the Munch Museum in Oslo, Norway, show changes in the position of the painting’s lone figure, resulting in the subjects being turned to face the viewer and being visually integrated with the scene. The successive changes show how Munch’s artistry transformed his hallucination into a significant and meaningful portrait of an emotional state of mind and reflected the artist’s own healthy creative processes.^[4]

6 Autoscopic Hallucination

An autoscopic hallucination is the perception of one’s own body or a part of it as existing separately and externally to the self. This type of hallucination occurred in conjunction with meningitis, seizures, space-occupying lesions, brain tumors, migraine, delirium, and post-traumatic brain lesions.

The Russian novelist Feodor (also spelled “Fyodor” and “Fjodor”) Dostoevsky (1821-1881) was regarded as an abnormally high-strung personality and suffered from an unknown ailment that made him subject to hallucinations. Even as a child, he had auditory hallucinations. Once, while hiking through a forest, he heard a voice warn that a wolf was loose. As Joseph Frank recounts in Dostoevsky: The Seeds of Revolt 1821-1849, as an adult, the novelist confided, he had become the victim of some sort of strange and unbearably torturing nervous illness that he called “mystic terror.” For a time, the novelist was convinced that someone who snored shared his bed. He had other hallucinations as well.

In fact, the second Mr. Golyadkin featured in the novel The Double may have been inspired by an autoscopic hallucination experienced by Dostoevsky himself. In any case, it is clear Dostoevsky’s “first-hand acquaintance with hallucinatory phenomena and his exceptional talent” allowed Dostoevsky to verbalize and analyze such experiences.^[5]

5 Hypnagogic Hallucinations

The English novelist Charles Dickens (1812-1879) experienced hypnagogic hallucinations, defined as fleeting perceptual experiences during the transition from wakefulness to sleep. Such incidents are often associated with involuntary and imagined experiences, hypnagogic hallucinations, and hypnopompic hallucinations (in the period from sleep to wakefulness). Dickens was also an insomniac.

His characters experience similar conditions and hallucinations, including insomnia, sleep promotion, hypnagogic hallucinations, perhaps the first report of restless legs syndrome, sleep paralysis, dreams, nightmares, terror, and drowsiness. One example of Dickens’s literary depiction of a hypnagogic hallucination appears in A Christmas Carol, as Ebenezer Scrooge is visited by four ghosts, leaving Scrooge unsure whether they are a dream or reality. A second example is that of Oliver Twist, who, when he falls asleep, “sees his enemies, Monks and Fagin, apparently in an episode of dream-reality confusion.”^[6]

4 Archangels and the Face of God

At age four, the poet, painter, and printmaker William Blake (1757-1827) saw God’s face through a window of the child’s house. About six years later, he said he saw a tree full of angels, their “bright angelic wings bespangling every bough like stars.” Later, archangels would dictate poetry to him and infuse the themes of his visual art. Blake’s hallucinations, which occurred again and again throughout his life, also included audible voices—those of his dead brother, to whom he spoke every day, and of angels.

A retroactive diagnosis of Blake suggests that he may have suffered from bipolar disorder or temporal lobe epilepsy. This latter condition could explain his seeing “ecstatic aurae,” such as those that typically indicate the presence of deities or angels in paintings and drawings.^[7]

3 Brobdingnagian Hallucination

As Jan Dirk Blom points out in A Dictionary of Hallucinations, the Gulliverian hallucination, aka the brobdingnagian hallucination, refers to a macroptic hallucination in which a human figure or figures are seen as disproportionally large. Terms like “lilliputian hallucination,” which involves the perception of tiny human figures, were inspired by Jonathan Swift’s novel Gulliver’s Travels.

Swift (1667-1745) experienced symptoms akin to those of Ménière’s disease, including cognitive changes, memory impairment, personality alterations, language disorder, and facial paralysis during the last three years of his life. And it is thought that the novel’s gigantic inhabitants of Brobdingnag and tiny people of Lilliput are based on Swift’s own visual hallucinations.^[8]

2 Hallucinations of the Sane

Whoever has seen The Garden of Earthly Delights must have wondered what, besides the fervent religious beliefs of Hieronymus Bosch (c. 1450s-1516), inspired the paintings. To say that they are bizarre and perverse characterizes the triptych in relatively mild terms.

Strange architecture, part floral and part stone; hybrid creatures; nude men and women performing acrobatics or sexual acts or riding horses, camels, mules, boars, bulls, and unicorns; huge fruits; lovers trapped inside clam shells, transparent floral bodies, and glass tubes; flowers in strange places—these are only some of the surreal images in the central panel of the triptych, which shows scenes of an earthly paradise awash in lust, preceding the even-worse pictures reserved for the right panel’s depiction of hell.

Roger Blench, author of “The hallucinatory Hieronymus Bosch: Charles Bonnet syndrome?” briefly assesses the possibility that Bosch’s imagery is related to episodes of Charles Bonnet Syndrome [CBS], aka “hallucinations of the sane.” Although Blench dismisses attempts to pigeonhole Bosch according to any one interpretation, he also suggests that there is evidence to see the artist’s work as Bosch’s own hallucinations transferred to canvas framed in an iconography acceptable to his era. According to this interpretation, Bosch wanted to express his paintings’ themes in at least an ostensibly Roman Catholic worldview that could be viewed as doctrinal, if unusual.^[9]

1 Hell, Purgatory, and Heaven

In Dante Alighieri (c. 1265-1321), we meet a poet whose work is nearly as strange and surreal, if not as obscure, as Bosch’s Garden. It wouldn’t be surprising to find that Dante’s epic depiction of the poet’s journey through hell (The Inferno), purgatory (Purgatorio), and heaven (Paradiso) was based, at least in part, on the poet’s own hallucinations. Indeed, such may very well have been the case, as it has been theorized the author may have had narcolepsy.

In The Divine Comedy, the poet Dante references his fictional counterpart’s sleep, weariness, dreams, and, as Dante himself writes, “rested eyes.” These allusions are explained as indications that the actual Dante suffered from both narcolepsy and catalepsy. The former is a neurological disorder. It interferes with the body’s regulation of sleep-wake cycles, causing sleepiness during the day and the tendency to nap for brief periods during waking hours. The latter condition causes muscular rigidity and unresponsiveness to the stimuli of the objective world.

The fictional Dante’s entire journey through hell, purgatory, and heaven is marked by sudden wake-dreaming transitions, short and refreshing naps, visions and hallucinations, unconscious behaviors, episodes of muscle weakness, and falls which are always triggered by strong emotions. The evidence that Dante is writing from experience about the hallucinations implied by his poetry is there in The Divine Comedy itself, in the behavior of its protagonist, the fictional Dante.^[10]