Laughter is good for your health (From helpguide.org)

Laughter relaxes the whole body. A good, hearty laugh relieves physical tension and stress, leaving your muscles relaxed for up to 45 minutes after.

Laughter boosts the immune system. Laughter decreases stress hormones and increases immune cells and infection-fighting antibodies, thus improving your resistance to disease.

Laughter triggers the release of endorphins, the body’s natural feel-good chemicals. Endorphins promote an overall sense of well-being and can even temporarily relieve pain.

Laughter protects the heart. Laughter improves the function of blood vessels and increases blood flow, which can help protect you against a heart attack and other cardiovascular problems.

Info Source: http://helpguide.org/life/humor_laughter_health.htm