mass psychogenic illness
Folie à deux – Shared psychosis, a psychiatric syndrome in which symptoms of a delusional belief are transmitted from one individual to another (from the French for "a madness shared by two") Herd mentality – Human tendency to adopt beliefs and behaviors favored by one's group Sick building syndrome – Health concern, where people in a building suffer from symptoms of illness or become infected with chronic disease from the building in which they work or reside