I've lost my ability to stay awake for days on end

I automatically shut off at midnight and wake up at 7AM, and there's nothing I can do about it. It's not that I'm getting old, I hope, but steady work has forced my body to conform to this bizarre new schedule. When I was a student I could stay up for 48hrs straight, sleep 5 hours, and feel fine. Maybe if I go back to school while working full time, I'll regain my ability to stay up for days on end. Or, maybe it'll have the opposite effect. At least I'll learn how to sleep standing up.