Question: Why am I awake at 6:34 AM on my day off?

Answer: Because I woke up an hour ago out of a dead sleep and haven't been able to fall asleep again. I woke up at 8 AM yesterday. Why can't I sleep in anymore?

Theory: Perhaps I've become so used to not getting enough sleep that my body has become convinced that seven hours is sleeping in. Which would be great if I felt completely rested at the end of it. But I don't. I'm still tired, deep down. I just can't do anything about it.