Zeuxis was a painter in the fifth century BC, who had been commissioned to paint a portrait of a wealthy patron as Aphrodite. When he saw the finished product, he supposedly laughed until he died. He was the first historical person to die laughing, but not the last. How dangerous can laughter really be?
The most direct death by laughter reported is supposedly audiologist Ole Bentzen who, while watching A Fish Called Wanda, laughed uncontrollably. His heart beat rose to "between 250-500 times per minute" until he died. An audiologist named O Bentzen does seem to have published a lot of papers on hearing aids, but there's no paper confirming his death other than the Weekly World News.
A man who died watching a comedy show called The Goodies reportedly died laughing, but he was suffering from a severe, hereditary heart condition. No one who has "laughed themselves to death" has been in good health, so it doesn't appear that laughter alone can kill anyone.
What can it do, then? Laughter can trigger cataplexy, a condition that leaves a person conscious but unable to move their muscles. However, the cataplexy comes first. Laughter can trigger it, but not cause it. Laughter can trigger syncope, i.e. fainting. This is an expected outcome whenever someone hyperventilates for too long. They're laughing, they grow lightheaded, they faint. One paper on the subject could be a comedy by itself:
We present a case of a 29-year-old previously healthy man who had witnessed a coworker trip and hit his head on the sink at approximately 10 a.m. He subsequently went into a severe fit of uncontrollable laughter that involved leaning forward and crouching down, at which point he began to feel lightheaded and dizzy. He collapsed for 3 seconds with definite loss of consciousness and nonspecific arm twitching. He regained consciousness within those 3 seconds and was oriented properly and prepared to resume his work duties.
I'm sure the coworker was just dying to help him out. (Another great thing about this paper is it's called "Laughter Induced Syncope: No Laughing Matter." Oh, I beg to differ in this case.)
Things can get worse. Some people have "gelastic seizures," gelastic being the medical term for laughter. People start laughing, or sometimes crying, and can't control themselves. These seizure can be the result of tumors, lesions, or other kinds of brain damage.
Losing control of laughter can be scary. Some people feel like they're smothering and are going to die as they black out, but still can't stop laughing. And laughter, doctors seem to agree, can be deadly to people with existing medical problems. Anything that puts a strain on the body, even if it's good, can be deadly. But it probably shouldn't stop you from watching A Fish Called Wanda.