What is the origin of the word "berserk"?

Search: berserk origin

Why: In Margot at the Wedding:

She's really berserk. Maybe it's hormones

Answer: It comes from the word berserker and the Icelandic form berserkr, which referred to "savage Norse warriors" (and elite Vikings). The word may be made up of ber, "bear" + serkr "shirt or coat," and maybe these guys wore intimidating bear-fur coats into battle.

Or ber might mean "bare," aka shirtless, aka naked.

Another fact that makes this theory plausible, is the side effect of the Amanita Muscaria, the Toadstool or Berserkers mushroom that they consumed to achive their aggrivated state. Along with the dementia and hallucinations, it causes profuse sweating, all the more reason to discard clothing.

Source: Word Detective, Answerbag

The More You Know: The fits of madness a berserker experienced were known as berserkergang. A description:

Men who were thus seized performed things which otherwise seemed impossible for human power. This condition is said to have begun with shivering, chattering of the teeth, and chill in the body, and then the face swelled and changed its color. With this was connected a great hot-headedness, which at last gave over into a great rage, under which they howled as wild animals, bit the edge of their shields, and cut down everything they met without discriminating between friend or foe. When this condition ceased, a great dulling of the mind and feeble- ness followed, which could last for one or several day.

Some believe Grendel was not a monster behaving like a man, but rather a man behaving like a monster, i.e. a berserker. Read the Viking Answer Lady's essay on it here.