Breathe in, breathe out, close your eyes, visualize a warm sunny beach, feel the heat on your body, feel your toes relaxing, then your arches, then your ankles ... and so on until you're pretty much asleep. Wake up eventually. If you're still stressed, then try smashing something cheap, noisy, and expendable (chipped plates will do fine). Then start over from the top.

And otherwise ... what everybody else has said.