In a web-based survey of 201 people who experience sleep paralysis, the side of the body on which vestibular-motor hallucinations—such as floating, flying, out-of-body experiences, and illusory movement—occur is linked to handedness and footedness. Left-right preferences for limbs predicted the side bias of these hallucinations, consistent with the idea that they arise from a vestibular, motor, and bodily-self neuromatrix. Intruder hallucinations—sensing a presence or seeing or hearing an alien agent—showed no such association with handedness or footedness, supporting the view that they stem from a separate threat-activated vigilance system.
Sleep paralysis often involves vivid hypnagogic and hypnopompic experiences (HHEs) that closely resemble supernatural assault narratives across cultures. A three-factor structural model explains these experiences through REM neurophysiology. The Intruder factor involves sensed presence, fear, and hallucinations from midbrain hypervigilance. The Incubus factor includes chest pressure and breathing difficulties from motoneuron hyperpolarization affecting respiration perception. Both imply an alien 'other' consistent with occult narratives. The Unusual Bodily Experiences factor involves floating, out-of-body sensations, and bliss from conflicts between endogenous and exogenous activation related to body position. These findings connect to hallucinations in hypnosis and schizophrenia.