We use the terms "bad dream" and "nightmare" almost synonymously. I contend that this is a frightfully naïve perspective. When we wake from a nightmare, we shortly realize that the floor isn't made of spiders, that all of the clowns are safely at the circus. But a dream in which we are happy... ah! Such a dream can color the real world world a darker shade long after the dreamer has awoken. These are truly the bad dreams.