The students, mostly female and all friends, began experiencing involuntary jerks and tics. Sometimes their limbs, neck or face would suddenly spasm; other times they would twitch, grunt, or shout.
Doctors and officials from the Health Department, the Centers for Disease Control and Prevention, and Columbia University could find no biological basis for the symptoms. The school was also checked for mold, lead, carbon monoxide, and other environmental contaminants; those tests also came back negative.
Mass hysteria, sometimes referred to as mass psychogenic illness or epidemic hysteria, more commonly effects women than men and there have been several incidents worldwide throughout history.
The Tanganyika laughter epidemic began on January 30, 1962, at a mission-run boarding school for girls in Kashasha, Tanzania. 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.
In October 1965 at a girls’ school in Blackburn, several girls complained of dizziness and some fainted. Within a couple of hours, 85 girls from the school were rushed by ambulance to a nearby hospital after fainting. Symptoms included swooning, moaning, chattering of teeth, hyperpnea, and tetany. A medical analysis of the event about one year later found that outbreaks began among the 14-year-olds, but that the heaviest incidence moved to the youngest age groups. There was no evidence of pollution of food or air.
It has also been suggested that recent outbreaks of feared Taliban poisoning in Afghanistan may in fact simply be cases of mass hysteria.