Mass Hysteria 

A condition affecting a group of persons, characterized by excitement or anxiety, irrational behavior or beliefs, or inexplicable symptoms of illness

An example of mass hysteria happened in 1994 when Gloria Ramirez was taken to a hospital because she was suffering from the effects of her cervical cancer. Any medical staff that treated her soon felt ill and began to faint. after blood test were run it was determined that there was nothing wrong with Gloria and everyone was just suffering from a case of mass hysteria.

Picture from: http://littlespyeye.wordpress.com/2012/09/09/the-toxic-lady-gloria-ramirez/