If you have ever been to Vegas you may have heard the urban legend about casinos pumping oxygen through the air conditioning system to help gamblers stay awake.  Though the fact that they do this has been proven false many times, the idea behind it stands true.  Deep breathing has been shown to increase energy levels.  Increased oxygen consumption also releases endorphins in the brain making it helpful for stress and pain management.  Simply pick a number (preferably higher than 5), breathe in for said number, hold the breath for 2 counts, breathe out for said number, hold the breath for 2 counts.  Repeat, increasing the number as you go.  Try this for a few minutes and see if it helps.  Work up to 10 minutes a day, or more if you like!