The night hag or old hag is the name given to a supernatural creature, commonly associated with the phenomenon of sleep paralysis. It is a phenomenon during which a person feels a 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/or supernatural character.