parasomnia

noun

para·​som·​nia ˌpar-ə-ˈsäm-nē-ə 

: any of various disorders of sleep characterized by abnormal behavioral or physiological activity (such as sleepwalking or night terrors) during sleep or in the transitional stage between sleep and wakefulness

There is a group of phenomena known as parasomnias, unpleasant physical activities that can occur when someone is in twilight state between deep sleep and wakefulness.

—H. Lee Kagan, Discover

The REM parasomnias are harder to explain. One, called sleep paralysis, is so terrifying that it has been blamed for reports of demon visitations and alien abductions.

—Ann Finkbeiner, New Scientist