Events of mass hysteria have happened multiple times in history. This is defined as a spontaneous reaction to a collective delusion. Mass hysteria mainly occurs in small groups who often spend a lot of time together. The hysteria aspect can spread quickly throughout a group or population, but the cause of the hysteria can change. 

The nuns who meowed like cats

 A convent in France dealt with a bizarre case of mass hysteria back in the middle ages. It all started with one nun who started to meow, and the others followed suit. In the Catholic church, cats are closely associated with the devil. Naturally, outsiders began to believe that the women were possessed. It got so bad that soldiers were brought in to "whip" them until they stopped.

The deadly dancing plague

This instance of mania is probably the most well-known in history. The dancing mania happened in July of 1518. Disease and famine had swept through France, leaving people starving, sick, and poor. One day, a woman named Torffea began to dance in the street. She danced for one week straight by herself. After that, others began to join her. By August, nearly a month later, over 400 people were silently dancing in the streets.

Doctors were baffled because they had no idea what would cause this non-stop silent dancing. Eventually, people began to die from heat exhaustion. They were forcibly removed from the streets.

The Tanganyika laughers

Laughter can be infectious, but things took a turn in 1962. Three young girls who lived in a boarding school in Tanzania randomly began to laugh uncontrollably. They laughed for hours at a time. The laughter spread to the other children and quickly became widespread. There were 217 of the "laughing flu" in the area. Most of the affected were school children. Within five months, it spread so much that 14 schools had to close down. 

The Halifax Slasher Panic

On November 16th, 1938, two women went to a local police station in Halifax, England, and reported that a man had attacked them with a razor blade. Both women were bleeding from their heads. The police went back to the alleged scene of the crime but found no evidence of an attack. Days later, more people came forward who also had cut and knife wounds reporting the same thing. Groups of men prowled the streets to find the slasher and attacked anyone who they deemed suspicious. 

During questioning, one victim claimed that they injured themselves after hearing about the first incident. Soon after, more victims admitted to injuring themselves. Nine of the 12 victims who had come forward admitted that they self-harmed. It's unclear why these people decided to partake in the panic.