Where does the word nightmare come from?

The Anglo-Saxon word mare is sometimes defined as a monster or spirit, and it was believed by some that such creatures sat on sleepers’ chests at night and stopped their breathing. In ancient Egypt, the small-statured, jovial god Bes was supposed to protect sleepers from nightmares. Likenesses of the god were hung in the bedroom or sometimes even carved into the headboard or bedposts to prevent inauspicious dreams. “Night hags” and “husbands (or wives) of the night” were other terms used for nightmares.