Also referred to as sleep-onset nightmare. The term hypnagogic nightmare is indebted to the Greek words hupnos (sleep) and agein (to lead, to transport). It is used to denote a type of " nightmare occurring during sleep onset (i.e. during stage N1 sleep as recorded on the electroencephalogram). Hypnagogic nightmares typically take the form of frightening " hypnagogic hallucinations which interrupt the process of falling asleep and lead to a sudden return to the state of full wakefulness.
References
Hartmann, E. (1984). The nightmare. The psychology and biology ofterrifying dreams. New York, NY: Basic Books.
Dictionary of Hallucinations. J.D. Blom. 2010.