the.com/anaphylaxis

means A severe, whole-body allergic reaction that can rapidly affect breathing and blood pressure and turn life-threatening within minutes.

from Coined in the early 1900s from Greek ana- ('against' or 'backward') plus phylaxis ('protection, guarding'). Researchers studying immunity had expected repeated small doses of a substance to build up protection, like a vaccine — instead, in some cases, a second dose triggered a violent reaction. So they named the phenomenon the opposite of protection: anaphylaxis, protection turned against the body.