A version of a daydream , only instead of fantasizing about when you get off work or a love interest or the clouds floating by your office or classroom window your stuck dreading the real situations you'll have to deal with later i.e breaking up , dentist visit, undesirable social event etc.
My daydream of being Scarlet Johannsen's boyfriend was rudely interrupted by my daydread of realizing I have to go to dinner at my in-laws...