1. out of control with anger or excitement; wild or frenzied:"a man went berserk with an arsenal of guns"
Word Originearly 19th century (originally as a noun denoting an ancient Norse warrior who fought with wild or uncontrolled ferocity): from Old Norse berserkr (noun), probably from birn-, bjorn (see bear2) + serkr ‘coat’, but also possibly from berr ‘bare’ (i.e. without armour).
In the Old Norse written corpus, berserkers were those who were said to have fought in a trance-like fury, a characteristic which later gave rise to the modern English word berserk. Wikipedia