If laughter is the best medicine, are there harmful side effects?

An article by R. E. Fermer and J. K. Aronson titled Laughter and MIRTH (Methodical Investigation of Risibility, Therapeutic and Harmful): Narrative Synthesis appeared in the Christmas 2013 issue of the British Medical Journal. You can read it in full here at PubMed Central. Their objective was to review both the beneficial and harmful effects of laughter.

Benefits of laughter included:

A] Reduced anger, anxiety, depression, and stress
B] reduced tension (psychological and cardiovascular)
C] increased pain threshold
D] reduced risk of myocardial infarction (presumably requiring hearty laughter)
E] improved lung function
F} increased energy expenditure
G] reduced blood glucose concentration

Harmful effects were:
A] Syncope (fainting)
B] cardiac and esophageal rupture
C] protrusion of abdominal hernias (from side splitting laughter or laughing fit to burst)
D] asthma attacks
E] interlobular emphysema
F] cataplexy
G] headaches
H] jaw dislocation
I] stress incontinence (from laughing like a drain)

Their conclusion was that:

Laughter is not purely beneficial. The harms it can cause are immediate and dose related, the risks being highest for Homeric (uncontrollable) laughter. The benefit-harm balance is probably favourable. It remains to be seen whether sick jokes make you ill or jokes in bad taste cause dysgeusia, and whether our views on comedians stand up to further scrutiny.

Increased energy expenditure sounded promising, but an article from 2007 on the Energy Expenditure of Genuine Laughter said that the effect is relatively small. It will not replace exercising or going on a diet.

The same image that appeared in Fermer and Aronson’s article is at Wikimedia Commons.