I've been doing it lately.
After nearly two weeks of sleeping until between 1 and 4 in the afternoon, this has been my surprising awakening schedule the past three days:
Saturday: 10am
Sunday: 9am
Monday: 6am
None with the aid of an alarm clock (I set them for all three of these days, but wake up way before them).
It's weird, and I don't understand it, especially considering last night I went to bed at 2am. Maybe my body is so used to being deprived of sleep that when I set an alarm, my brain keeps it in the back of my mind, and it instinctively wakes up four hours after I fall asleep. In fact, now that I think about it, there may be some truth to this theory. I did fall asleep around 4-5am on Friday and Saturday nights. When my brain knows it doesn't have to wake up for anything (regardless of the time) it sleeps for as long as my body can handle. When it knows it does have to wake up, it sleeps for four hours and then wakes up.
What a terrible situation to be in...