Sleep paralysis is paralysis associated with sleep that may occur in healthy persons or may be associated with narcolepsy, cataplexy, and hypnagogic hallucinations. The pathophysiology of this condition is closely related to the normal hypotonia that occurs during REM sleep. When considered to be a disease, isolated sleep paralysis is classified as Medical Subject Headings. Some evidence suggests that it can also, in some cases, be a symptom of migraine.
Symptoms and characteristics
Physiologically, sleep paralysis is closely related to REM atonia, the paralysis that occurs as a natural part of REM (rapid eye movement) sleep. Sleep paralysis occurs either when falling asleep, or when awakening. When it occurs upon falling asleep, the person remains aware while the body shuts down for REM sleep, and it is called hypnagogic or predormital sleep paralysis. When it occurs upon awakening, the person becomes aware before the REM cycle is complete, and it is called hypnopompic or postdormital. The paralysis can last from several seconds to several minutes, with some rare cases being hours, "by which the individual may experience panic symptoms" (described below). As the correlation with REM sleep suggests, the paralysis is not entirely complete; use of EOG traces shows that eye movement is still possible during such episodes.
In addition, the paralysis may be accompanied by terrifying hallucinations, perceived deafening loud noise and an acute sense of danger. Sleep paralysis is particularly frightening to the individual because of the vividness of such hallucinations. The hallucinatory element to sleep paralysis makes it even more likely that someone will interpret the experience as a dream, since completely fanciful or dream-like objects may appear in the room alongside one's normal vision. Some scientists have proposed this condition as an explanation for reports of alien abductions and ghostly encounters. Some authors have warned of the possible misconnection between child sexual abuse and hypnagogic/pompic phenomena and have noted that some clients after having described such an event to a fortune teller or psychic that the psychic may have suggested CSA.
In surveys from Canada, China, England, Japan and Nigeria, 20% to 60% of individuals reported having experienced sleep paralysis at least once in their lifetime. A study conducted by Sedaghat-Hamedani F. et al. has investigated the prevalence of sleep paralysis among Iranian medical students. 24.1% of students reported experiencing sleep paralysis at least once in their lifetime. Comparable results were reported among Japanese, Nigerian, Kuwaiti, Sudanese and American students.<
Many people who commonly enter sleep paralysis also suffer from narcolepsy.
Some reports read that various factors increase the likelihood of both paralysis and hallucinations. These include:
- Sleeping in a face upwards or supine position
- Increased stress
- Sudden environmental/lifestyle changes
- A lucid dream that immediately precedes the episode.
- Excessive consumption of alcohol coupled with lack of adequate sleep.
In The Terror That Comes in the Night, folklorist and behavioral scientist David J. Hufford argues that sleep paralysis is related to an anomalous experience known in Newfoundland as "the Old Hag." According to Hufford, the Old Hag is "an experience with stable contents which is widespread, dramatic, realistic, and bizarre," and elements of the phenomenon cannot be fully explained either by psychology or culture. His works have explored the connection between the Old Hag and parapsychology in what he labels the "experience-centered approach" to hauntings.
Treatment starts with patient education about sleep stages and about the muscle atonia that is typically associated with REM sleep. It is recommended that patients be evaluated for narcolepsy if symptoms persist.