There's an interesting article at the NYTimes by James Gorman entitled: "Scientists Hint at Why Laughter Feels So Good" and it begins thusly:
Laughter is regularly promoted as a source of health and well being, but it has been hard to pin down exactly why laughing until it hurts feels so good.
The answer, reports Robin Dunbar, an evolutionary psychologist at Oxford, is not the intellectual pleasure of cerebral humor, but the physical act of laughing. The simple muscular exertions involved in producing the familiar ha, ha, ha, he said, trigger an increase in endorphins, the brain chemicals known for their feel-good effect."
This is why I regulalry laugh at nothing. Here comes a dust bunny! I'm brought to my knees! Here's the sound of water gurgling in the drain. I laugh til I can't stand it and have to put a bag filled with lilac petals and feathers over my head. This calms me just long enough to find the couch.
But you see it has to be nothing. I don't find the comedians funny. They work too hard. I don't think cruelty is funny.
Ah but here comes a piece of paper which flew off my desk because there was evaporation from the sea and the wind came next, all the way from Jutland and by God I can't stand it! I'm the happiest man alive! Just here. In an empty room. And the beuaty is, no one can steal it.