A joke that somebody tells when they first wake up that makes no sense. They come up with it in their sleep, and in accordance with all dream rules and regulation, it makes sense when they are half awake. The humor and logic of the joke usually wears off mid-speak, but because they started the joke, they have to finish it. It is usually replied to with looks of concern, or looks that convey, "What the *&%^ are you on?"
In contrast, the jokes can sometimes be funny if the person you tell it to has experience with the situation you talk yourself into.
Josh: Yeah, sure, bro. Good morning, by the way.
Jack: Yeah, good morning. K, here goes: Why can't you put fruit in wells? *puzzled face*
Josh: I dunno, why?
Jack: Wait, never mind, it doesn't make any sense.
Josh: No, c'mon man you can't just start a joke and not finish it! Spit it out!
Jack: Uhhhh. . . 'cuz uh. . . they are star fruit?
Eruption of laughter
Josh: Dude, that had to be a dream joke!
Jack: Definitely. Sorry bro. Hey is that coffee done yet?