Paroxysm is from the Greek word paroxysmos, which basically means "to irritate." If you're irritated to the point of having a wild fit, like if you see someone trying to steal your car, you might go into a paroxysm of rage. When the teacher talked about private parts, the students went into a paroxysm of giggles. A paroxysm can be medical, too, like when an illness suddenly attacks, and you get symptoms like chills and a fever right away.