I don't sleep well. Usually my body only wants 6 to 7 hours regardless of what I did the day before and then my eyes pop open and there is no going back. If I don't go to sleep when my body tells me, I'll miss my chance. And by miss my chance, I mean I wont feel sluggish anymore and I'll be awake, though giggly, for another five to six hours. It seems to build up after a bit and I'll drift into a heavy 13-15 hour sleep once a week (or so). Like I'm catching up.
It helps when I have a normal schedule. But I am currently on a night schedule AND trying to get through The Witcher 2, that leaves errands and chores to be done - and all that is just,....destroying my inner-clock. lol