Mass hysteria — other names include collective hysteria, group hysteria, Mass Psychogenic Illness, or collective obsessional behavior — is the sociopsychological phenomenon of the manifestation of the same or similar hysterical symptoms by more than one person. A common manifestation of mass hysteria occurs when a group of people believe they are suffering from a similar disease or ailment.
Mass hysteria typically begins when an individual becomes ill or hysterical during a period of stress. After this initial individual shows symptoms, others begin to manifest similar symptoms, typically nausea, muscle weakness, fits or headache.
The features of mass hysteria include no plausible cause found, ambiguous symptoms, rapid escalation of cases - often spread by line of sight - and rapid remission of symptoms. Demographically, cases are higher in females and those with greater use of medical services. Other factors that contribute to the severity of the symptoms and spread are protective clothing worn by emergency services and mistaken or misleading investigations.
Sightings of religious miracles are often attributed to mass hysteria.
In 2009 in Fort Worth, Texas, 34 people were sent to the hospital after they complained about having symptoms when they mistakenly thought they had been exposed to carbon monoxide.
In 2008 in Tanzania, about 20 female school pupils began to faint in a schoolroom, collapsing to the floor and losing consciousness, while others after witnessing this sobbed, yelled and ran around the school. A local education officer was quoted in news reports saying that such events are "very common here"