Sleep paralysis is a condition that occurs in the state just before dropping off to sleep (the hypnagogic state) or just before fully awakening from sleep (the hypnopompic state). The condition is characterized by being unable to move or speak.
It is often associated with a feeling that there is some sort of presence, a feeling which often arouses fear but is also accompanied by an inability to cry out. The paralysis may last only a few seconds. The experience may involve visual, auditory, or tactile hallucinations.
Humming, roaring, hissing, rushing and buzzing noises are frequent in conjunction with sleep paralysis (SP). This happens when the REM atonia sets in sooner than usual, before the person is fully asleep, or persists longer than usual, after the person has (in other respects) fully awoken. Sleep paralysis is reportedly very frequent among narcoleptics. It occurs frequently in about 6% of the rest of the population, and occurs occasionally in 60%. 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.
The paralysis itself is frequently accompanied by additional phenomena. Typical examples include a feeling of being crushed or suffocated, electric ‘tingles’ or ‘vibrations’, imagined speech and other noises, the imagined presence of a visible or invisible entity, and sometimes intense emotion: fear or euphoria and orgasmic feelings.Sleep paralysis has been proposed as an explanation for at least some alien abduction experiences and shadow people hauntings.
The description of the symptoms of sleep paralysis is similar to the description many alien abductees give in recounting their abduction experiences. Sleep paralysis is thought by some to account for not only many alien abduction delusions, but also ghost sightings and delusions involving paranormal or supernatural experiences (e.g., incubus and succubus). People who have experienced sleep paralysisi also report on feeling that there is someone or something in the room with them, they hear footsteps and other unsourced noises too.