Situational factors affecting sleep paralysis and associated hallucinations: position and timing effects

Sleep paralysis (SP) is a temporary inability to move or speak when waking up or falling asleep, often accompanied by frightening hallucinations. Two studies involving 6730 subjects, including 4699 who had experienced SP, examined how body position and timing affect SP. More individuals reported SP while lying on their back (supine) than in all other positions combined. The supine position was three to four times more common during SP than during normal sleep. SP episodes occurring in the middle or at the end of sleep were more likely to involve the supine position than those at the beginning, suggesting later episodes may arise from brief awakenings during REM sleep possibly triggered by apnea.

Study at a glance

Abstract

Sleep paralysis (SP) entails a period of paralysis upon waking or falling asleep and is often accompanied by terrifying hallucinations. Two situational conditions for sleep paralysis, body position (supine, prone, and left or right lateral decubitus) and timing (beginning, middle, or end of sleep), were investigated in two studies involving 6730 subjects, including 4699 SP experients. A greater number of individuals reported SP in the supine position than all other positions combined. The supine position was also 3–4 times more common during SP than when normally falling asleep. The supine position during SP was reported to be more prevalent at the middle and end of sleep than at the beginning suggesting that the SP episodes at the later times might arise from brief microarousals during REM, possibly induced by apnea. Reported frequency of SP was also greater among those consistently reporting episodes at the beginning and middle of sleep than among those reporting episodes when waking up at the end of sleep. The effects of position and timing of SP on the nature of hallucinations that accompany SP were also examined. Modest effects were found for SP timing, but not body position, and the reported intensity of hallucinations and fear during SP. Thus, body position and timing of SP episodes appear to affect both the incidence and, to a lesser extent, the quality of the SP experience.