I never heard of a “laughter epidemic” before. From Wikipedia
The Tanganyika laughter epidemic of 1962 was an outbreak of mass hysteria – or mass psychogenic illness (MPI) – rumored to have occurred in or near the village of Kashasha on the western coast of Lake Victoria in the modern nation of Tanzania (formerly Tanganyika) near the border of Kenya.
The laughter epidemic began on January 30, 1962, at a mission-run boarding school for girls in Kashasha. The laughter started with three girls and spread haphazardly throughout the school, affecting 95 of the 159 pupils, aged 12–18. Symptoms lasted from a few hours to 16 days in those affected. The teaching staff were not affected but reported that students were unable to concentrate on their lessons. The school was forced to close down on March 18, 1962.
HT goes to this interesting article on the Guardian (on why people laugh)