Two-stage relaxation. First is to work out any anxiety that the stress has caused. Exercise, angry music(yell/scream along if you feel comfortable doing so), punching a wall, whatever helps drain some energy from you. Then, switch to a low gear. Soft music, a warm bath, pictures of fluffyness. It works wonders.
You could also scream until you pass out. That's surprisingly effective, though rather stupid and dangerous.