It’s called “shock”. When your body experiences extreme trauma like a car accident, it goes into survival mode by pumping you full of adrenaline, blocking pain receptors and even shutting out some of what’s happening around you so that you can get away from the danger and survive. This developed in the days before medical care was even a concept and we only had ourselves. You can’t maintain that state forever though and when it wears off you get to experience everything, plus deal with the side effects of your body going into overdrive
Latest Answers