Mare (folklore)
A mare (Old English: mære; Danish, Norwegian: mare; Swedish: mara; Polish: mara, zmora; among many others) is a malicious entity in Germanic and Slavic folklore that sits, walks, or "rides" on people's chests while they sleep, bringing on nightmares.
Source: Wikipedia, Mare (folklore). Text licensed CC BY-SA 4.0. Not endorsed by or affiliated with Wikipedia or the Wikimedia Foundation.