When I sleep, I lack an internal clock.

[Les Waste]

I learned about this in psychology

You probably have no real reason to wake up in the morning, so you don't. Everyone who doesn't have some severe brain damage can wake up at almost any time without an alarm clock. If you have to be at work by 7, so you need to wake up by 6, you can get up without an alarm clock by 6.

But if you don't have any reason to wake up by a certain time, you're body will just keep sleeping until it physically can't sleep any more as opposed to waking up whenever you need to be up by, which is why you can feel more tired after sleeping for 12 hours than you will if you sleep for 4 hours.

I don't know if that's true, but after I learned about it I was able to force myself to get up every morning without my alarm clock. Now, about 95 percent of the time, I wake up about 5 to 10 minutes before my alarm clock goes off, and I never even need it to go start screaming at me.