"Laughter is a socially noble orgasm"
It seems that laughter and the related emotions, releases energy with healing effects in the human organism. Norman Cousins had devoted many years from his life to study and prove it. (see
http://en.wikipedia.org/wiki/Norman_Cousins )
Similar healing effects have also feelings of gratitude. For this effect of laughter most of the great teachers of personal development agree, including Tony Robbins, and masters of NLP.
I have read the next unbelievable story: A married woman about 35 years old is diagnosed with terminal breast cancer. The doctors give her 6 months of life. She refuses to try chemotherapy, as essentially her cancer is diagnosed terminal. So in order at least to enjoy her last months of life, she takes her small children and goes daily to watch in cinemas 2-3 comedy films. After 3 months she goes again to monitor her disease. The doctor is talking of miracle cure, the tumours have almost disappeared!
If cancer can be cured with large doses of laughter, then we can imagine the effect on less serious diseases.