A phenomenon in which social trauma or anxiety combines with a suspicious event to produce psychosomatic symptoms, such as nausea, difficulty breathing, and paralysis. If many individuals come to believe that the psychosomatic outbreak is connected to the cause of the trauma or anxiety, these symptoms can spread rapidly throughout a population.
In December 2005 a mysterious illness marked by headache, fever, faintness, and numbness in extremities occurred in 13 school children in the Shelkov region of Chechnya. Many believed the illness was caused by a Russian chemical weapons attack, which precipitated the rapid spread of similar symptoms throughout the region. Medical officials determined the episode was a case of psychosomatic contagion—mass psychogenic illness—brought on by anxiety over Russian military activities in the area. There is no evidence the illnesses were caused by chemical weapons.
https://file.wikileaks.org/file/dhs-mass-psychogenic-illness-2006.pdf