PENN STATE (US) — Students and psychiatric patients are more likely than others to experience sleep paralysis, a rare condition that can include hallucinations about alien abductions and demons.
Sleep paralysis, a condition that affects less the 8 percent of the general population, is defined as “a discrete period of time during which voluntary muscle movement is inhibited, yet ocular and respiratory movements are intact,” according to a new study in the current issue of Sleep Medicine Reviews.
Some experts now suspect the townspeople involved in the Salem witch trials may have been experiencing sleep paralysis. And in the 19th-century novel Moby Dick, the main character Ishmael experiences an episode of sleep paralysis in the form of a malevolent presence in the room.
Some people who experience these episodes may regularly try to avoid going to sleep because of the unpleasant sensations they experience. But other people enjoy the sensations they feel during sleep paralysis, notes Brian A. Sharpless, clinical assistant professor of psychology at Penn State.
“I realized that there were no real sleep paralysis prevalence rates available that were based on large and diverse samples,” Sharpless says. “So I combined data from my previous study with 34 other studies in order to determine how common it was in different groups.”
He looked at a total of 35 published studies from the past 50 years to find lifetime sleep paralysis rates. These studies surveyed a total of 36,533 people. Overall he found that about one-fifth of these people experienced an episode at least once. Frequency of sleep paralysis ranged from once in a lifetime to every night.
When looking at specific groups, 28 percent of students reported experiencing sleep paralysis, while nearly 32 percent of psychiatric patients reported experiencing at least one episode. People with panic disorder were even more likely to experience sleep paralysis, and almost 35 percent of those surveyed reported experiencing these episodes. Sleep paralysis also appears to be more common in non-Caucasians.
“Sleep paralysis should be assessed more regularly and uniformly in order to determine its impact on individual functioning and better articulate its relation to other psychiatric and medical conditions,” Sharpless says.
He looked at a broad range of samples—papers were included from several different countries.
People experience three basic types of hallucinations during sleep paralysis—the presence of an intruder, pressure on the chest sometimes accompanied by physical and/or sexual assault experiences, and levitation or out-of-body experiences.
There has been little research conducted on how to alleviate sleep paralysis or whether or not people experience episodes throughout their lives.
“I want to better understand how sleep paralysis affects people, as opposed to simply knowing that they experience it,” says Sharpless. “I want to see how it impacts their lives.”
Sharpless hopes to look at relationships between sleep paralysis and post-traumatic stress disorder in the future.
Jacques P. Barber, professor of psychiatry at the University of Pennsylvania, contributed to the research, which was supported in part by the National Institute of Mental Health.
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