Why can't I ever sleep in when I fall asleep drunk?

Is it just me, or is there a physiological explanation for this? I’ve had this problem for years. I have no trouble falling asleep at 10 pm on a weeknight either dead sober or a bit tipsy, but if I get pretty drunk and try to fall asleep at 3 am or so… I am just incapable of sleeping more than 6 hours.