Same thing happens to me. Get drunk on a Friday or Saturday night, go to bed anywhere between 2 and 4 AM, and wake up ready to go around 8:30 or 9. I'm too used to waking up in the morning for work, so I think my body is just used to it.
I find that alcohol actually helps me fall asleep. Ever since I was a kid, I've had a real hard time falling asleep. I can't just lay down and be snoozing within 10 minutes. It seriously takes me hours sometimes. And when I do fall asleep, I sometimes wake up every half hour throughout the night. Except when I drink though. Once I've got 10-12 beers in me, I can, and sometimes do fall asleep anywhere.