Breathing to De-Stress
Yogis have known how to use the breath to control their bodies for donkeys. It's very effective in either revving you up or calming you down. If meditation isn't your thing, then breathing is a super easy way to get you grounded and calm again.
Are you breathing correctly in the first place? When you breathe in your belly should expand. When you breathe out it comes back in. Loads of people did it the other way round and don't even realise. Give it a try.
Slowing the breath tells your brain you're not in danger. It then triggers the parasympathetic nervous system response - your heart rate slows, your blood pressure drops, the cortisol (stress hormone) response turns off, you feel better. Try counting in for 6 and out for 6. To really get it to work, start to make the exhale last even longer.
Nice article in the NY Times on the benefits of controlling the breath.