Ryan Singel summarizes a memo produced at the Department of Homeland Security:
Americans' fear of a terrorism could create a mass outbreak of a psychosomatic illness—even in the absence of any real attack—creating a fake epidemic that could overwhelm hospitals attempting to treat real victims.
Adding to the confusion, the symptoms of a mass pyschogenic illness look much like symptoms of an anthrax attack, avian flu outbreak or chemical attack.
The report was originally issued in 2006 and recently revealed on Wikileaks. To download it in pdf form, go here.