Be Pain Free made a good point -- clutter can really stress you out. You begin to feel like your world is closing in on you with all the stuff! Sell some or give it away!
Also, exercise and stretching is a great way to relieve stress, tension, and gain energy we didn't know we had. Being able to move your body will give you a sense of control over it, and a calmness that no matter what happens throughout the day, you can handle it.