Night hag

It is a phenomenon in which the sleeper feels the presence of a supernatural, malevolent being which immobilizes the person as if sitting on their chest or the foot of their bed.

The original definition of sleep paralysis was codified by Samuel Johnson in his A Dictionary of the English Language as nightmare, a term that evolved into our modern definition.

Such sleep paralysis was widely considered the work of demons, and more specifically incubi, which were thought to sit on the chests of sleepers.

In Old English the name for these beings was mare or mære (from a proto-Germanic *marōn, cf.

The word might be etymologically cognate to Greek Marōn (in the Odyssey) and Sanskrit Māra.