Hypnopompic Sleep Paralysis, Sleep Paralysis, Hypnopompic, Sleep, Paralysis, Hypnagogic, narcolepsy
Sleep paralysis is a phenomenon during which an individual is unable to move during falling asleep or awakening, but is aware of their surroundings. It is often accompanied by frightening hallucinations to which one is unable to react because of paralysis and perceived physical experiences, such as a strong current running through the upper body. Sleep paralysis poses no immediate risk to those who experience it, although it occasionally causes significant distress. Episodes last from several seconds to several minutes.
Genetics and sleep deprivation are a major cause of sleep paralysis, and it has also been linked to disorders such as narcolepsy, migraines, stress, anxiety disorders, trauma and obstructive sleep apnea. Sleeping in a fixed supine position increases the chance of sleep paralysis. The underlying mechanism is believed to result from disrupted REM sleep when there should be a general inability to move muscle to prevent the sleeper from acting out their dreams.
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 from sleep. When it occurs upon falling asleep, the person remains aware while the body shuts down for REM sleep, a condition called hypnagogic or preterminal sleep paralysis. When it occurs upon awakening, the person becomes aware before the REM cycle is complete, and it is called hypnopompic or postorbital.
Between 8% and 50% of people experience sleep paralysis at some point in time.