Berserker Shift

Berserker Shift: occurs when a person has the "ability to induce a state of possession by his kindred beast, acquiring its strength, fearlessness, and fury." Trances and altered states of consciousness are methods to enter a berserk shift, most commonly used by warriors for the purpose of going into battle. This is arguably not related to Therianthropy. There are discussions around the term on AHWW throughout the 1990's, but most were to explain the term's origins in Norse mythology and explain that emotions, anger, and rage are human traits.

See also: Shift (Therianthropic)

Feral Shift - Alternative

Feral Shift might be a more accurate term, in that it means a person is having a full mental shift due to strong emotions such as anger that completely pushes away the human side temporarily. However, shifts are never an excuse to lash out at someone and cause harm. Self control is still possible and should be practiced during all shifts. This form of shift is rarely experienced or discussed in the community.

Origins

Berserker comes from Old Norse berserkir meaning “bear-shirts”. Another related term is úlfheðnar (pronounced “oolv-HETH-nahr” with a hard “th” as in “the") which is Old Norse for “wolf-hides”.

"These names are a reference to the practice of dressing in a ritual costume made from the hide of the totem animal, an outward reminder of the wearer’s having gone beyond the confines of his humanity and become a divine predator."

It is highly recommend that you read more about the Norse origins of these terms to better understand them. See the link in the first reference below.