I used to have a lot of trouble staying awake in classes at times. I found that it helps to have something to do with my hands - knitting or doodling.

Also, I second the suggestion of AM exercise. I was probably at my healthiest and most stable when I was getting a half-hour of circuit training at 6 AM every day. It really wakes me up and makes the rest of the day go a lot better - it's just really hard to make myself do it.