Mass delusion

In sociology and psychology, mass hysteria (also known as collective hysteria, group hysteria, or collective obsessional behavior) is a phenomenon that transmits collective illusions of threats, whether real or imaginary, through a population in society as a result of rumors and fear (memory acknowledgment).

In medicine, the term is used to describe the spontaneous manifestation (production in chemicals in the body) of the same or similar hysterical physical symptoms by more than one person.

A common type of mass hysteria occurs when a group of people believe they are suffering from a similar disease or ailment, sometimes referred to as mass psychogenic illness or epidemic hysteria.

A nun of a French convent inexplicably began to meow like a cat, shortly leading to the other nuns in the convent also meowing. Eventually all the nuns would meow together for a certain period every day, leaving the surrounding community astonished. This did not stop until the police threatened to whip the nuns.

A nun in a German convent began to bite her companions, and the behavior spread through other convents in Germany, into Holland and as far as Italy.

The Dancing Plague of 1518 was a case of dancing mania that occurred in Strasbourg, Alsace (then part of the Holy Roman Empire) in July 1518. Numerous people took to dancing for days without rest, and, over the period of about one month, some of the people died from heart attack, stroke, or exhaustion.

The Irish Fright took place in England and parts of Wales in December 1688 during the Glorious Revolution. False reports that Irish soldiers were burning and massacring English towns prompted a mass panic in at least nineteen counties, with thousands of people arming themselves and preparing to resist non-existent groups of marauding Irishmen.

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