I've experienced burnout a number of times in personal and professional contexts and I think nearing 30, I've got a pretty good handle on myself finally.
1. You can ALWAYS and should ALWAYS talk to SOMEONE. My advice is find a great therapist. If you can't afford one, you need to find a friend, confidant, or family member that's away from the action. Talk through things and see if you can wrap your head around what's bothering you.
2. Exercise. Seriously. Exercise helps sleeps, weight loss, anxiety, depression, add--it's a pretty awesome medication. Read "Spark" by John Ratey.
3. Sleep. The times in my life I've felt most burnt out corresponded with awful sleeping patterns. (also see 2)
4. Reflect. After trying to talk through things and getting your body back on track think about your work. Are you happy doing what you're doing? Do you want to do something else? (some might recommend doing this first--I wouldn't; only because in my judgment I've made decisions I regretted because I felt like I wasn't in the right place--not because I really didn't like the opportunity)
This is obviously a reader's digest version, but it took me probably 5 or 6 iterations before I could identify, prevent (or treat) my burnout.