From what I gather from the Internet, the what made the viking berserkers fight so ferociously and appear to be indestructible,at least until after the battle, at which point they usually died which is present in several myths--one such example would be the death of beowulf, as well as Grendel's immunity to edged weapons and his death after leaving heorot-- was a combination of what is now known as PTSD/TBI, amanita mushrooms, and the exhaustion rituals. My question is what could these rituals looked like? Are there any surviving traditions of this practice?