This word describes the state of mind one often experiences just as you fall asleep or as you are beginning to wake up. It covers a range of various sometimes strange perceptual experiences by the half-asleep person, such as a conscious awareness of dreaming while dreaming or the “Tetris Effect”-reliving aspects of a repetitive task that engrossed you during the day (like playing Tetris).
Some people experience paralysis that could include a feeling of weight on the chest, an unknown or recognized presence in the room, and/or various sights, sounds or other sensory perceptions.
It is proposed that hypnagogic phenomena can account for the perceptions that some people interpret as actual alien abductions, hauntings, etc.