This happens to be a lot when I'm anxious. However I see the good side in it (somehow). If it is only a few hours of sleep, my body takes it as a refreshing nap of a sort and is prepped up (My internal alarm clock even wakes me up at the right time!). This has happened for as long as I remember. The only penalty is being tired the night of (Which is a good thing). Good luck to you though!