The night hag or old hag is the name given to a supernatural creature, commonly associated with the phenomenon of sleep paralysis. The Old Hag occurs in the lore of England and Scotland. She is also found in both Canadian and American folklore as an import. She evidently derives from the original Anglo-Saxon mare.
She is described as a witch whose soul leaves her body at night and then victimizes a normal person asleep.
According to some of this lore, she would ride upon her victim into the sky.
It became known as 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.
People suffering from repeated attacks, lacking as much rest and energy in the morning as they did when they first fell asleep, were said to be “hag-ridden.” People suffering debilitating diseases such as tuberculosis were also sometimes thought to be hag-ridden.