The night hag is the name given to a supernatural creature, commonly associated with the phenomenon of sleep paralysis. 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 word "night-mare" or "nightmare" was used to describe this phenomenon before the word received its modern, more general meaning. Various cultures have various names for this phenomenon and supernatural character.