Conversion disorder (formerly "hysteria") is a psychosomatic illness. The patient will present with any of a number of neurological symptoms that generally will not disappear with treatment. Unlike Munchausen syndrome, the patient is not deliberately feigning the symptoms and is of the genuine belief that they are ill. It is generally caused by severe stress or personal conflict. It can mimic many other illnesses, some of them quite severe. Conversion disorder can affect a large number of people at once, particularly in very stressful situations, (colloquially "mass hysteria").