A thing which has survived from the past. A let down after a period of excitement. Hanging over can mean what is left from a unanswered question or scene as in a movie. Hangover Square is a book written by Patrick Hamilton.
Hangover is the drowsy effect one has in a day (usually when the person is inactive/down/doll. especially sitting down listening to a sermon at church) after being stressed or exhausted on the previous day.