So smile, you'll feel better. Keep smiling, you'll get well sooner. Laugh and you have just increased your chances of not getting sick in the first place. Laughter also improves a person's sense of well being and energy level by increasing oxygenation. When ATP is increased, one's energy level is increased as well.
Laughter has the same effect on the body as exercise or aerobics.
This means that the individual walking down the street laughing is getting close to the same work out as the person jogging by. Humor that produces laughter provides physiologic benefits through improving oxygenation and energy levels. Laughter stimulates the skeletal, facial, abdominal and thoracic muscles. It pulls it up again. Mosby's Pharmacology in Nursing.