One of the simplest things possible to do for your health doesn't involve finding time to exercise, weighing every ounce of food, or taking multiple vitamin capsules three times a day. It is done simply by mindfully intensifying something you do as a matter of course, thousands of times a day.
I know for me, if I wake up in pain, it somehow dulls the pain and increases my energy to take ten deep breaths before even trying to get out of bed.
If I am having a bad day and am unable to complete my usual exercises, simply breathing helps to burn calories. The more oxygen (within reason, no hyperventilating) I can give my system, the more calories I am able to burn. Unless I am having an asthma attack or something, I can breathe every minute of every day :-}
A quick internet search turned up several articles with more information, if you are interested (all from Associated Content):
Too Tired? Take a Deep Breath
Breathing Deeply to Reduce Anxiety
Yoga Breathing to Reduce Stress
Easy Breathing to Reduce Blood Pressure
Benefits of Abdominal Breathing
photo is of Oscar and Amanda (and a wee Sean still in Amanda) hugging one of the trees creating oxygen in the Gaylord, Michigan area