Brian A. Sharpless, clinical assistant professor of psychology at Penn State, said 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.
"I realized that there were no real sleep paralysis prevalence rates available that were based on large and diverse samples," Sharpless said in a statement. "So I combined data from my previous study with 34 other studies in order to determine how common it was in different groups."
Sharpless and colleagues reviewed 35 published studies from the past 50 years to find lifetime sleep paralysis rates involved 36,533 people. Overall the review found that about one-fifth of these people experienced an episode at least once.
The study, published in the journal Sleep Medicine Reviews, found 28 percent of students reported experiencing sleep paralysis, while nearly 32 percent of psychiatric patients reported experiencing at least one episode.
The witch trials in Salem, Mass., are thought possibly to involve the townspeople experiencing sleep paralysis, while in the novel "Moby Dick," the main character Ishmael experiences an episode of sleep paralysis in the form of a malevolent presence in the room.