Sleep Paralysis and Anomalous Experience
Sleep paralysis is a transient inability to move or speak that occurs at the boundary between sleep and wakefulness, while the person is conscious and aware of their surroundings. It arises when the muscle atonia of rapid eye movement (REM) sleep persists into, or intrudes upon, wakefulness, so that the mind is awake while the body remains in the immobilized state normal to dreaming sleep 1,3. Episodes are brief, usually lasting from seconds to a few minutes, and are often accompanied by vivid sleep-state imagery and intense fear. Clinicians classify the phenomenon as a REM parasomnia and describe it as a state dissociation, an overlap in which features of REM sleep and features of waking occur at the same time 3,4.
What happens during sleep paralysis
REM atonia and state dissociation
During normal REM sleep the brain actively suppresses skeletal muscle tone. This atonia prevents the sleeper from physically acting out dreams. In sleep paralysis, consciousness returns before that suppression lifts. The clinical reference StatPearls describes the condition as one in which "resumption of consciousness occurs while muscle atonia of REM (rapid eye movement) sleep is maintained, leading to intense fear and apprehension in the patient as the patient lies awake without the ability to use any part of their body" 3. Reviews frame this as a dissociated state in which REM processes and wakefulness coexist rather than alternating cleanly 4. The person can typically move the eyes and breathe, but voluntary movement of the limbs, trunk, and voice is blocked.
Hypnagogic and hypnopompic imagery
Sleep paralysis is frequently accompanied by vivid perceptions. When they occur as a person is falling asleep they are termed hypnagogic. When they occur on waking they are termed hypnopompic 1. Because REM dream imagery can continue while the person is aware and paralyzed, the resulting impressions can be exceptionally vivid and are experienced as real events in the room rather than as dreams. One researcher describing the state to the Harvard Gazette called it "dreaming with your eyes wide open" 5.
The three clusters of sleep paralysis experiences
The experiences reported during sleep paralysis are not random. Work by J. Allan Cheyne and colleagues in the late 1990s identified three recurring factors, or clusters, of experience 1,4. The intruder and incubus clusters tend to co-occur and carry the threatening, fearful quality most associated with the state, while the third cluster, vestibular-motor experience, is often described in neutral or even pleasant terms 4.
| Cluster | Core experiences | Common interpretation |
|---|---|---|
| Intruder | A felt presence, fear, and auditory or visual imagery. It includes the sense that someone is in the room | An intruder, ghost, demon, or in modern accounts an alien at the bedside |
| Incubus | Pressure on the chest, difficulty breathing, smothering or choking, and a sense of assault | A malevolent being sitting or pressing on the sleeper, read historically as the Old Hag or a demon |
| Vestibular-motor | Floating, flying, spinning, falling, out-of-body experiences, and sometimes bliss | Levitation or being lifted and transported, described in abduction accounts as being floated from the bed |
The felt presence, a strong sense that some being is nearby even when nothing is clearly seen, is one of the most consistently reported features and belongs primarily to the intruder cluster 4. The incubus cluster centers on pressure on the chest, difficulty breathing, and a sensation of being smothered or assaulted 1,4. The vestibular-motor cluster, sometimes labelled unusual bodily experiences, includes floating and out-of-body sensations and is the cluster that most often carries a positive rather than a frightening tone 4.
How common is sleep paralysis?
Estimates of how many people experience sleep paralysis vary widely because studies use different definitions and samples. The most cited figure comes from a 2011 systematic review by Brian Sharpless and Jacques Barber, published in Sleep Medicine Reviews, which aggregated 35 studies covering 36,533 participants 2. Across the general population they found a lifetime prevalence of 7.6 percent, meaning roughly one person in thirteen reports at least one lifetime episode. Rates were substantially higher in specific groups: 28.3 percent among students and 31.9 percent among psychiatric patients, rising to 34.6 percent among patients with panic disorder 2.
Other surveys report higher figures, in part because a single lifetime episode is common and easy to elicit. Susan Blackmore, writing in 1998, noted that isolated sleep paralysis occurs in a large minority of the population, with international surveys ranging widely by country 6. A 2017 review summarizing this literature concluded that about one in five individuals may have experienced sleep paralysis at least once 4. The consistent finding across methods is that the experience is common in the general population and is not in itself a marker of illness 2,5.
Isolated sleep paralysis, narcolepsy, and management
Clinicians distinguish isolated sleep paralysis, which occurs on its own in otherwise healthy sleepers, from sleep paralysis associated with narcolepsy and other sleep disorders 1,3. When episodes happen independently of any diagnosed condition or substance use, the term is isolated sleep paralysis. When they recur frequently, it is sometimes called recurrent isolated sleep paralysis 1. Sleep paralysis is one of the classic features of narcolepsy, and an estimated 30 to 50 percent of people diagnosed with narcolepsy report experiencing it 1.
Reported risk factors include sleep deprivation and irregular schedules, sleeping in the supine (face-up) position, stress and trauma exposure, anxiety disorders, alcohol use, and a family history of the experience 3. There is no established treatment for an episode already in progress. StatPearls states plainly that "to date, there is no direct treatment strategy to treat sleep paralysis during an active episode" 3. Clinical management focuses on reassurance about the benign nature of isolated sleep paralysis, improving sleep hygiene and sleep duration, and treating any underlying disorder 3,4. Approaches under study include cognitive-behavioral techniques adapted for the condition and, in one report, focused-attention meditation combined with muscle relaxation. REM-suppressing antidepressants are sometimes used off-label where episodes are frequent and distressing 3,4.
Historical development
Long before sleep paralysis had a clinical name, cultures across the world recorded the experience and interpreted it as the visitation of a supernatural being. The English word nightmare preserves one such interpretation. The "mare" in nightmare derives from Old English and older Germanic roots naming a demonic entity believed to sit on the chest of a sleeper and cause a feeling of suffocation 1. In Newfoundland folklore the experience is called the Old Hag, and to be "hagged" or "hag-ridden" is to be pinned and pressed by a witch or crone during the night 1.
Similar figures recur widely. The incubus and succubus of medieval European demonology, the pressing spirits of many folk traditions, and a range of night-visitor beings across cultures each map onto the same recognizable pattern of paralysis, chest pressure, and a felt malevolent presence 1. The best-known artistic depiction is Henry Fuseli's 1781 painting The Nightmare, which shows a sleeping woman with a squat demon crouched on her chest and is widely read as a portrayal of sleep paralysis interpreted as demonic visitation 1.
Sleep paralysis in contact literature
From the 1980s onward, as accounts of contact and abduction entered popular culture, several researchers proposed that sleep paralysis could account for recurring features of some nighttime reports. The classic bedroom narrative includes waking at night unable to move, sensing a presence, seeing figures at the bedside, feeling pressure or examination, and floating or being lifted. These elements correspond closely to the intruder, incubus, and vestibular-motor clusters of sleep paralysis 1,6. That overlap makes the state one serious candidate context for such episodes, while the experiencer literature also records encounters that do not fit this profile.
Psychologist Susan Blackmore set out this argument in a 1998 essay. She described the core sleep paralysis experience as one in which "a person wakes up paralyzed, senses a presence in the room, feels fear or even terror, and may hear buzzing and humming noises, or see strange lights," and argued that "the best explanation for many abduction experiences is that they are elaborations of the experience of sleep paralysis" 6. Blackmore suggested that a person familiar with media images of aliens may interpret the felt presence as an extraterrestrial, and she reported that her own survey data did not reproduce the widely publicized Roper survey estimate that millions of Americans had been abducted 6.
At Harvard, psychologists Susan Clancy and Richard McNally studied people who reported being abducted. In their findings, these individuals scored higher than comparison groups on measures of hypnotic suggestibility, absorption, magical ideation, and dissociative experiences 7. In a 2002 study in the Journal of Abnormal Psychology, Clancy, McNally, and colleagues also reported heightened susceptibility to memory distortion in this group 7. In their later analysis, including a 2005 paper on sleep paralysis, sexual abuse, and space alien abduction, they concluded that many of the reports they studied began in episodes of sleep paralysis whose waking imagery was later interpreted, often through hypnosis and memory-recovery sessions, as memories of abduction 5,7. Clancy set out her perspective for a general audience in her book Abducted: How People Come to Believe They Were Kidnapped by Aliens, published by Harvard University Press 5. The researchers stressed that experiencers were sincere and not mentally ill. The Harvard Gazette summarized their view that the state is "as normal as hiccups" 5. Reviews in this research tradition further argue that hypnosis, frequently used to elicit these accounts, actively shapes the narratives rather than simply retrieving them, a methodological point that experiencer researchers also weigh when evaluating hypnotically assisted testimony 7.
A separate line of evidence comes from deliberately induced encounters. In a 2021 study in the International Journal of Dream Research, Michael Raduga, Andrey Shashkov, and Zhanna Zhunusova instructed 152 experienced lucid dreamers to try to find or summon aliens or UFOs during a lucid dream 8,9. Of the volunteers, 114, or 75 percent, reported experiencing such encounters after one or more attempts. About 61 percent met alien-like beings, 28 percent encountered UFOs, and roughly 24 percent felt fear or sleep paralysis during the attempt 8,9. Around one in five described the experience as close to reality 8. The authors concluded that people might spontaneously encounter similar events during REM sleep and confuse them with reality, though they noted that the study was conducted online and relied entirely on self-report 8,9.
Taken together, this body of work offers a well-documented framework for understanding why many nighttime contact reports share the same structural features. It does not, on its own, establish that every abduction account originates in sleep paralysis, and it does not address reports that occur during full waking activity away from bed 6,7. Those accounts remain part of the experiencer record and merit study on their own terms.
Overlap is not equivalence
Sleep paralysis can overlap with some nighttime experiences, but overlap does not establish that all contact accounts arise from the same source. The state is defined by specific conditions. It occurs at the boundary of sleep, in bed, in a single percipient, and it ends with ordinary waking. Reports that fit that profile can reasonably be studied alongside it.
Many entries in the contact and abduction record involve circumstances the sleep paralysis profile does not address. These include events observed outdoors or from vehicles, daytime encounters, episodes involving several witnesses at once, persistent physical context such as marks on the ground or interrupted equipment, recordings made during the event, and experiences that begin well outside sleep transitions. For cases of this kind, sleep research provides background rather than an answer, and their study belongs to the contact researchers who gather firsthand testimony. Treating overlap as equivalence would close questions that the record leaves open.
Leading interpretations
These interpretations are not mutually exclusive, and each is held by serious researchers.
| Interpretation | Core claim | What it requires to be true |
|---|---|---|
| Neurological state dissociation | Sleep paralysis is REM atonia and REM imagery intruding into wakefulness, producing the paralysis, pressure, and felt presence. | The reported features map onto known REM physiology, which the clinical and review literature supports. |
| Cultural interpretation of a universal experience | The same bodily event is read through locally available figures: the mare, the Old Hag, the demon, the alien. | A single recognizable experience appears across cultures under many names, which the folklore and historical record documents. |
| Overlapping context for some reports | Some abduction, ghost, and intruder reports are elaborations of sleep paralysis episodes shaped by expectation. | The phenomenology of those reports matches the sleep paralysis clusters, and priming shapes interpretation, as the psychological research indicates. |
| Literal external encounter | At least some reports describe a real external being or event rather than a sleep phenomenon. | Corroboration independent of testimony, which experiencer researchers continue to seek and which remains an open line of inquiry. |
Documentation and research record
The clinical record is extensive. Sleep paralysis is a recognized REM parasomnia, its prevalence has been measured across dozens of studies, and its phenomenology has been mapped into stable factors through questionnaire research 1,2,4. The record connecting it to anomalous experience was built from several directions: survey and phenomenological work by Blackmore, interview and laboratory studies of experiencers by Clancy and McNally, and induction research with lucid dreamers by Raduga and colleagues 6,7,8. Alongside this clinical and psychological documentation stands the experiencer record itself, decades of first-person testimony gathered by contact researchers, which includes bedroom episodes matching the sleep paralysis profile as well as waking encounters that do not. Demonstrating that sleep paralysis can generate an intruder-and-levitation narrative does not determine the origin of any particular report, and the clinical research does not speak to encounters described outside the sleep-wake boundary. The clinical picture is documented. The interpretation of any single contact report is not settled by it, and that judgment rests with those who examine each account in full.
The record and open questions
Documented: Sleep paralysis is a REM parasomnia in which REM muscle atonia persists into wakefulness. Its lifetime prevalence in the general population is about 7.6 percent by the most cited systematic review, and it is higher among students, psychiatric patients, and people with narcolepsy. Its characteristic experiences cluster into intruder, incubus, and vestibular-motor types, and the experience has been interpreted through supernatural figures across many cultures for centuries 1,2,4.
Reported: People describe waking paralyzed, sensing a presence, feeling crushing pressure on the chest, and floating or being lifted. In modern Western settings some experiencers describe these episodes as contact or abduction events, and historical traditions read the same pattern as the Old Hag, the incubus, or the mare 1,6. The experiencer record also includes encounters reported during full waking activity, which the sleep paralysis profile does not cover.
Open questions: Whether any individual report reflects sleep paralysis, another identified cause, or something not yet understood cannot be settled from the general finding. Sleep paralysis accounts for the shared structure of many nighttime reports without determining the origin of any single case, and accounts arising outside the sleep-wake boundary fall outside its scope 6,7. These remain genuinely open questions, and the investigators closest to these accounts keep working on them.
Frequently asked questions
What causes sleep paralysis?
Sleep paralysis occurs when the muscle atonia of REM sleep persists into wakefulness, so the mind is awake while the body remains in the immobile state of dreaming sleep. Common triggers include sleep deprivation, irregular sleep schedules, sleeping face-up, stress, and, in some people, narcolepsy 1,3.
Is sleep paralysis dangerous?
Isolated sleep paralysis is not physically dangerous and is not a sign of mental illness. Episodes are brief and end on their own. Clinical guidance centers on reassurance, better sleep habits, and treating any underlying sleep disorder 3,5.
Why do people see a figure or feel a presence during sleep paralysis?
The sense of a nearby being, called the felt presence, and the sight of a figure belong to the intruder cluster of sleep paralysis experiences identified by Cheyne and colleagues. Because REM dream imagery continues while the person is awake and paralyzed, these figures are experienced as real and are often frightening 1,4.
How does sleep paralysis relate to abduction and contact accounts?
Researchers including Susan Blackmore, Susan Clancy, and Richard McNally have argued that sleep paralysis overlaps with many nighttime abduction reports, because the paralysis, presence, chest pressure, and floating match the state closely. Overlap is one possible context for some experiences, not a universal explanation, and accounts involving exterior events, multiple witnesses, or full waking activity fall outside its profile 6,7.
Can you trigger these experiences on purpose?
To a degree, yes. In a 2021 study, experienced lucid dreamers who were told to summon aliens or UFOs during a lucid dream reported encounter-like experiences at high rates, and about a quarter also felt fear or sleep paralysis during the attempt 8,9. The authors concluded that similar experiences might arise spontaneously during REM sleep, a finding that informs the discussion without closing it.
How do you stop sleep paralysis?
There is no treatment for an episode already underway, but frequency can often be reduced by getting enough sleep, keeping a regular schedule, avoiding the supine sleeping position, and limiting alcohol. Where episodes are frequent and distressing, clinicians may treat an underlying disorder or, less commonly, prescribe REM-suppressing medication 3,4.
Sources and further reading
- Wikipedia. "Sleep paralysis." https://en.wikipedia.org/wiki/Sleep_paralysis
- Sharpless, Brian A., and Jacques P. Barber. "Lifetime prevalence rates of sleep paralysis: a systematic review." Sleep Medicine Reviews, 2011. https://pmc.ncbi.nlm.nih.gov/articles/PMC3156892/
- Sharma S., et al. "Sleep Paralysis." StatPearls, NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK562322/
- "Sleep Paralysis: phenomenology, neurophysiology and treatment." Review preprint, arXiv:1704.02342, 2017. https://arxiv.org/pdf/1704.02342
- Cromie, William J. "Alien abduction claims explained." Harvard Gazette, September 2005. https://news.harvard.edu/gazette/story/2005/09/alien-abduction-claims-explained/
- Blackmore, Susan. "Abduction by Aliens or Sleep Paralysis?" Skeptical Inquirer, 1998. https://www.susanblackmore.uk/wp-content/uploads/2017/05/Abduction-by-Aliens-or-Sleep-Paralysis.pdf
- Wikipedia. "Perspectives on the alien abduction phenomenon." https://en.wikipedia.org/wiki/Perspectives_on_the_alien_abduction_phenomenon
- Raduga, Michael, Andrey Shashkov, and Zhanna Zhunusova. "Emulating alien and UFO encounters in REM sleep." International Journal of Dream Research, 2021. https://journals.ub.uni-heidelberg.de/index.php/IJoDR/article/view/78599
- Weisberger, Mindy. "'Alien abduction' stories may come from lucid dreaming, study hints." Space.com, July 2021. https://www.space.com/lucid-dreaming-ufo-alien-abductions
Categories: Culture, belief & history