Laughter is the best medicine, it alway helps. No matter how bad I feel, the extent of the pain, the prognosis it's all is made better by laughing. I take a shower, hop out, look in the mirror & just bust out in laughter. Sometimes I can't stop laughing, sad really. But who cares, go out & laugh, it takes less muscle & you'll feel better.
I think that when you laugh your body feels better. You're not as depressed or down on yourself. I don't think it can cure an actual problem, but you do feel better when happy and your body reacts better.