People say of a bit of humor or a comical situation that it was "hysterical" -- shorthand for "hysterically funny" -- meaning "hilarious." But when you speak of a man being "hysterical" it means he is having a fit of hysteria, and that may not be funny at all. Dictionary.com lists this as one of the definitions of "hysteria":
1. A neurosis characterized by the presentation of a physical ailment without an organic cause, such as amnesia.
2. Excessive or uncontrollable emotion, such as fear.