After 5am, if I've woken up, that's it - I can't go back to sleep without feeling even worse once I wake up again, so I might as well get up. Hunger usually compels me to get out of bed too, and a general restlessness - my mind wanders, and I get bored. I'm also a morning person; I don't like doing things in the afternoon. If I have anything to do, I get it done before midday.