to be a disorder
of only women
(thus the root words being hyster, as it was originally thought
that the uterus was a free floating object in a woman's body, and when lost would cause her to be hysterical), the original cure was for the doctor to masturbate the woman.
mostly it is characterized by uncontrollable emotion, be it amusement, fear, etc, in a given situation.
there was an outbreak of the plague, causing mass hysteria.