mostly it is characterized by uncontrollable emotion, be it amusement, fear, etc, in a given situation.
Stephanie or other friend nearby: "Oh God, she's going into hysteria again! Get the medication!"
an uncontrollable outburst of emotion or fear, often characterized by irrationality, laughter, weeping, etc
Psychoanalysis . a psychoneurotic disorder characterized by violent emotional outbreaks, disturbances of sensory and motor functions, and various abnormal effects due to autosuggestion.
A kick-ass Muse song.