Ack... I wouldn't recommend yoga myself. When I was doing it regularly, it had a tendency to GIVE me energy.
I actually find sudokus help me sleep... there's something relaxing about them, making all those numbers fit. Keep 'em nice and easy though, and if you find one that's not solving itself, skip it.
Calm music is good, housework is better. Oh, the lethargy from washing dishes.... ;)