Hi, I thought you may like this Mentalrobics exercise from Braingle.com:
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Breathing

The breathing pattern of someone who is under a lot of stress [ For more on 'stress' go here: http://www.braingle.com/mind/534.html ] is likely to be shallow and rapid. This type of breathing lowers the amount of oxygen that can get into your bloodstream and up to your brain. Decreased oxygen can cause dizziness, headaches and heightened feelings of stress. Learning how to breath properly is one of the most important things you can do to help relax yourself. It's for this reason that controlled breathing is a part of almost every type of meditation practiced in the world.

Proper deep breathing starts with your diaphragm. Instead of puffing out your chest, try to puff our your belly as you breathe. Use your entire lung capacity. Breath in through your nose and out through your mouth.

Whenever you feel stressed, take a full five minutes to concentrate on deep breathes. This type of breathing will increase oxygen flow to your brain and release endorphins and hormones that act to sooth your nerves.
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For more mind exercises: http://www.braingle.com/mind/