Scientists speculate that negative dreams are evolutionarily What Causes Nightmares adapting, purging the brain of memories or associations which trigger fear.

The victim mostly wakes with a innervation of terror, out-of-date difficulty breathing because of a perceived heavy invisible net on his or her chest, and is inadequate to stir i.e., experiences blanket drill paralysis. This nightmare inwardness is described as being "hag-ridden" in the Gullah lore