Mass hysteria is a phenomenon in which a group of people simultaneously exhibit similar hysterical symptoms. Technically, it involves physical effects, such as headache, nausea, dizziness, or a trance-like state or seizure-like movements. However, the term is also commonly used to refer to any mass delusion, in which a group of people become governed by irrational beliefs or moral panic.
Many cases of mass hysteria are controversial, as the supposed sufferers and even some observers feel that the term does not fully explain the phenomenon; for example, in the case of an alleged religious miracle or demonic possession affecting a large group of people. In addition, many people are reluctant to believe that intense physical symptoms they experienced were "all in their head."
This phenomenon is most common in small, close-knit communities, particularly if they are isolated. Enclosed areas such as schools, factories, and hospitals are typical settings. There are two main types of mass hysteria: anxiety hysteria and motor hysteria.
Anxiety hysteria is shorter in duration, typically lasting a day. Symptoms may include nausea, light-headedness, headache, dizziness, and physical weakness. Often, this type of mass hysteria begins with the complaint of a single member of the group of something like an odd smell in the room. Others pick up on a perceived threat and begin to exhibit psychosomatic symptoms.
Motor hysteria is characterized by nervous twitching or spasms, trance-like states, and histrionic outbursts. It is slower to manifest than anxiety hysteria, building gradually over a few days or weeks, but can take weeks or months to subside. Motor hysteria commonly has a more severe and longstanding cause than anxiety hysteria as well; for example, brutal living conditions or excessive discipline.
Mass hysteria has been documented since ancient times, though it was not understood until recently as a sociopsychological phenomenon rather than a supernatural one. Throughout history, it has frequently been the cause of moral panics that resulted in widespread rioting and even torture and executions, as in the case of witch hunts and trials. Even though the phenomenon is better understood today, it remains mysterious and disturbing, and those who have been subject to mass hysteria do not always find the modern psychological explanation sufficient.