Learn That Word

Synonyms for Berserk (same or very similar meaning)

WordNet sense 1 (one of the ancient Norse warriors legendary for working themselves into a frenzy before a battle and fighting with reckless savagery and insane fury):

WordNet sense 2 (in a murderous frenzy as if possessed by a demon):
amok, amuck, demoniac, demoniacal, possessed

WordNet sense 3 (afflicted with or characteristic of mental derangement):

From the ODE community, based on WordNetadd/edit