I was reading a post on another of my astronomy forums where the poster had intended staying up to see the comet but fell asleep while watching a DVD. The next thing he knew was that it was gone 5am and that his oversized pooch was busy licking his face!
I think I'd prefer to rely on an alarm clock.... Incidentally I find a kitchen timer useful when the weather is intermittently cloudy - set it for 15 mins and deliberately try to nap, check the sky when it goes off then either go & observe or reset the timer & nap some more ....