Aliens, Ghosts, and Old Hags: The Terrifying Mysteries of Sleep Paralysis

”A sensed presence, vague gibberish spoken in one’s ear, shadowy creatures moving about the room, a strange immobility, a crushing pressure and painful sensations in various parts of the body — these are compatible not just with an assault by a primitive demon but also with probing by alien experimenters, …And the sensations of floating and flying account for the reports of levitation and transport to alien vessels.”

Dr. J. Allan Cheyne, Associate Professor of Psychology at the University of Waterloo for The New York Times


From the southwestern deserts of the US to remote Japanese forest villages and across the span of recorded human history, there have been numerous accounts of nocturnally-based paranormal phenomena. In fact, “the ‘mare’ in ‘nightmare’ originally refer[s] to a demonic woman who suffocated sleepers by lying on their chests (she was called ‘Old Hag’ in Newfoundland).” (Sacks, 2012).

Dr. Cheyne summarizes these accounts into what he believes is the experience of sleep paralysis.  Isolated sleep paralysis (SP) is a REM associated parasomnia characterized by “a transient, conscious state of involuntary immobility occurring immediately prior to falling asleep or upon wakening” (Cheyne, 2003). The occurrence of this distinct phenomenon unrelated to the presence of medical conditions like narcolepsy and seizure disorders defines isolated SP (Sharpless and Grom, 2016). SP is not only peculiar it’s also quite common.  Sharpless and Grom (2016) cite a recent study showing at least one SP episode as prevalent in 7.6% of the general population, 28.3% of students, and 31.9% of psychiatric patients from a sample of 36,000. Meanwhile a UK study suggests between 25% to 40% of the general population experienced SP, though referred to as awareness during sleep paralysis (ASP) in the article (Holden and French, 2002).

The frightfulness, and imagery-vivid recall, of SP results from hypnagogic and hypnopompic experiences (HHEs). Hypnagogic and hypnopompic derive from the Greek meaning sleep leading and sleep procession, respectively. Hypnagogic refers to the acute sense of a heinous presence and the sensations of floating and chest pressure. Hypnopompic denotes the same sensations but experienced post-sleep, just preceding complete awakening (Holden and French, 2002).  Cheyne, Rueffer, and Newby-Clark (1993) extend the definition of HHEs to include sensations of suffocating, choking, floating, out-of-body, and flying as well as combinations of auditory and visual hallucinations. “Visual hallucinations may involve lights, animals, strange figures, and demons. [AH] may include heavy footsteps, humming or buzzing noises, and sounds of heavy objects being moved” (Holden and French, 2002).  Other bemusing features include the likelihood of SP occurring while lying supine in preparation for or the initial emergence from the sleeping state. There is a feeling of progressive bodily heaviness. Often the eyes are the only mobile body part (Holden and French, 2002) along with the muscles of respiration and audition (Higgins and George, 2013).

Turning to the physiology of REM sleep helps to better understand what makes SP so noteworthy.  Rapid eye movement (REM) sleep occurs in the deepest stage of slumber. The brain’s electrical activity mimics wakefulness during REM episodes. In non-REM (NREM) sleep ocular motion is minimal and involuntary homeostatic processes, like metabolic and heart rates are decreased.  PET studies show an idling brain in NREM sleep and muscular movement is possible. It is in REM sleep that skeletal muscles become atonic, autonomic activation is heightened, and the brain is essentially active and hallucinating. Though the dreaming brain visits all stages of sleep, REM sleep elicits a more “illogical, bizarre, and even hallucinatory” variety compared to the thought-based, problem-solving dreams of NREM sleep (Higgins and George, 2013).

When everything is going right in REM sleep you are indeed paralyzed, mostly likely hallucinating, and have brain activity akin to being conscious. Holden and French (2002) analysis of the literature seeks to expound on just what makes SP anomalous.  Thus far, most ideas around the physiology of SP are speculative. However, a 3-category neurological model has been posited to gain further insight into this parasomnia. The first category labeled ‘Intruder’ characterizes the “sensed presence, extreme fear, and [AVH]” believed to stem from lengthy amygdala analysis of the possible fear source. This analysis is minutes long versus the normal seconds long processing. The increased processing time only serves to increase the sense of fear. Seeking to understand the fear source, “endogenous [cues] (middle ear activity) or external stimuli (e.g., shadows or external sounds)” are pooled and become increasingly susceptible to hallucinatory interpretations.

The second category, ‘Incubus’, marks the sensations of chest pressure, dyspnea and pain. Gaining a level of consciousness during REM sleep means that you have, at least, semi-awakened in a body out of your control. Respiratory rate (RR) is increased involuntarily. The semi-conscious person may instinctively attempt to control their RR (by trying to breathe deeply) but fail. The brain may register this failure as chest pressure and pain. The last category, ‘Unusual Bodily Experiences’, include floating, flying and/or out-of-body sensations.  A paralyzed body can not appropriately interpret feedback from vestibular activation. Vestibular activation gives us information about our bodies position and orientation in space. Misinterpretations in this area can lead to sensations of floating or flying.  Receiving visual information from the environment in addition to the aforementioned sensations can play into the perception of being out of one’s body.  Cheyne et al.’s neurological model as summarized by Holden and French is the closest researchers have come to explaining SP, or more specifically HHEs.

The experience of sleep paralysis is terrifying and not wholly uncommon. There is a possibility that we will have patients who have experienced SP episodes.  This can include both isolated and repeated occurrences with demonic/alien hallucinatory features and without. We should first rule out the possibility of a concurrent sleep or seizure disorder. Advising patients to try and avoid sleeping on their backs is also a helpful intervention. It’s also helpful to know that any disruptions to the sleep routine can increase the insistence of SP including jet lag and daytime naps.  Depression-based intrusions to a sleep schedule is another common impetus (McNally and Clancy, 2005). Continued work in psychotherapy can also help attenuate SP episodes. Harvard researchers have discovered a correlation between childhood sexual abuse and higher rates of SP than those denying a history (McNally and Clancy, 2005; 2005). Early bodily trauma experiences increase the likelihood of dissociative episodes. A study showed that those with higher scores of dissociation had a corresponding increased likelihood of “unusual sleep-related experiences (e.g., flying dreams, hypnopompic imagery, sensing the presence of someone)” (McNally and Clancy, 2005). Keeping this information in mind, psychiatric care providers can use effective minimally invasive interventions to treat seemingly far out disturbances like SP.

Sweet dreams!


Cheyne, J. A. (2003). Sleep paralysis and the structure of waking-nightmare hallucinations. Dreaming, 13(3), 163-179.

Cheyne, J. A., Rueffer, S. D., & Newby-Clark, I. R. (1999). Hyponagogic and hypopompic hallucinations during sleep paralysis: Neurological and cultural construction of the night-mare. Consciousness and Cognition, 8, 319-337.

Higgins, E. S., & George, M. S. (2013). Sleep and circadian rhythms. In The neuroscience of clinical psychiatry: The pathophysiology of behavior and mental illness (2nd ed., pp. 174-187). Philadelphia, PA: Wolters Kluwer.

Holden, K. J., & French, C. C. (2002). Alien abduction experiences: Some clues from neuropsychology and neuropsychiatry. Cognitive Neuropsychiatry, 7(3), 163-178.

Kristof, N. D. (1999, July 6). Alien abduction? Science calls it sleep paralysis. The New York Times. Retrieved from

McNally, R. J., & Clancy, S. A. (2005). Sleep paralysis in adults reporting repressed, recovered, or continuous memories of childhood sexual abuse. Journal of Anxiety Disorders, 19, 595-602.

McNally, R. J., & Clancy, S. A. (2005). Sleep paralysis, sexual abuse, and space alien abduction. Transcultural Psychiatry, 42(1), 113-122.

Sacks, O. (2012). Hallucinations. New York, NY: Random House, Inc.


6 thoughts on “Aliens, Ghosts, and Old Hags: The Terrifying Mysteries of Sleep Paralysis

  1. This is really interesting, I really don’t know where I got the idea from I have always believed that bad dreams result from lack of sound sleep. Thank you for posting this I now have a new idea of what sleep paralysis is.

    Whenever I think of sleep paralysis, I think of these terrifying stories. I remember watching a history channel documentary on aliens and one of their explanations was sleep paralysis. I have experienced this phenom before but I have never seen anything “scary” like ghosts, aliens, or demons. I can tell you though its a very scary experience and this post confirms that i usually have these when I am sleep deprived.

  3. I think sleep is really cool to read about and study. I remember watching a movie called “Awake” where he was under anesthesia for surgery and could feel everything. I have no idea why I think of this when it comes to REM sleep and the paralysis. I agree with Joe as echo his experience when he is sleep deprived. Thanks for this Cristal! Very cool stuff.

  4. I found this so interesting. I have a patient in my geriatrics rotation who describes a dream that she had that she feels completely messed with her head. She told me that it felt incredibly real. My preceptor and I educated her on these events but I hadn’t realized that it could affect someone for such a long time. I also found it very interesting that it is linked to childhood trauma and dissociation. I have experienced both of those things and I have recently been wondering if nightmares I have are actually some sort of sleep paralysis. I will dream that I am either incredibly tired to the point of being unable to move, or that I have been drugged and am out of control. Great quotations!

  5. I loved how you brought the historical understanding of this phenomena into your blog post. I think it is fascinating to see how those who went before us understood these experiences. Something we see as a biological phenomena, was once thought to be an evil demon’s assault.

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