Dave Bagwill referred me to this entry from Zen Habits:
If you feel overwhelmed, breathe. It will calm you and release the tensions.
If you are worried about something coming up, or caught up in something that already happened, breathe. It will bring you back to the present.
If you are moving too fast, breathe. It will remind you to slow down, and enjoy life more.
Breathe, and enjoy each moment of this life. They’re too fleeting and few to waste.
Much good comes from daily, mindful, deep breathing. It is essential as a preliminary to meditation, but is also valuable throughout the day. Just remember to do it. In these hyperkinetic times, it is important to have at the ready various techniques for slowing done. For more on this theme, see my category Slow Down!
One needn't subscribe to the metaphysics of Zen Buddhism to make good use of its techniques.