Like any exercise, laughing relaxes you, and works against chronic stress that most Americans wear on the shoulder. Mehmet C. Oz, M.D., a heart surgeon at New York-Presbyterian Hospital/Columbia University Medical Center in New York City, explains why this is so in a 2005 “Reader’s Digest” article:
"When you push any engine, including your body, to its maximum, every once in a while it slips a gear. The ways the body manifests that are: irregular heartbeats, high blood pressure, and increased sensitivity to pain. When people use humor, the autonomic nervous system just tones down a bit to take it off high gear, and that allows the heart to relax."