sleep, always make me feel better in the morning. why dont u go out one night, u can take one night off and go out for a drink with ur mates, that always relaxes me.
Excercise is always good for relieving stress. It doesn't really have to be hard core either! A ten minute walk can often be enough to clear your head.
Also when you're getting that really stressed out feeling remember to take deep breaths and try to relax. It's alwful when you start to panic and you can feel your heart racing. Breathing more slowly should help to steady your heart rate a bit and physically relax you, so that mentally you can feel more calm.