A fictional disease which causes you to get tired at abnormally early hours during social situations when you have no reason to be tired. Therefore, the only explanation of your tiredness is that you must of contacted some kind of virus, most likely a STD, which causes drowsiness.
Brad: "Joe, wake up man. It's only 1 am and you're sitting there looking like you're about to fall asleep."
Joe: "Yeah, I'm tired for no reason. I think that black chick gave me Sleep AIDS."