When you're stressed or anxious, you breathe more shallowly. This can set up a downward energy spiral: If you're not breathing properly, you're not ferrying enough oxygen to your tissues, and that oxygen deficiency impairs energy metabolism. Shallow breathing also allows toxic metabolic waste to build up in your cells, he explains, making you feel sluggish and ill.
Take a deep breath -- or several. The best way to get more oxygen is to breathe slowly and deeply from your diaphragm, not your chest. Plus, take your mother's advice and sit up straight: Poor posture tires out your muscles and compresses your organs, so your body doesn't work as well as it should. Practicing yoga can help you cover both bases. Basic breathing exercises also help. A couple of times a day, sit with your spine straight, your eyes closed, and your abdomen relaxed. Take a breath in, imagining that you're filling the bottom of your torso -- let your belly expand -- then the middle, and finally the top. Exhale in reverse: top, middle, bottom. Repeat for 10 breaths.