I've had really bad stress levels at certain points in grad school. It mostly manifests in not being able to sleep, which I've never had any problems with at any other point in my life.
I've tried a bunch of things, but I think the things that helped the most were:
- Exercise
- Relaxing before bed - putting the books away and just trying to get my mind completely off school
- Staying up late if I'm feeling really stressed and think I'm going to have trouble sleeping; for me it's much better to just stay up and watch TV or surf the net than to lay in bed unable to sleep. That's exactly how I found this forum a few months back, lol.
- Meditation in bed. I learned some very basic meditation techniques that I use in bed. It helps clear my mind and makes a big difference in being able to fall asleep.