It was at school in the canteen and my friend asked me to show me a magic trick. So i said "ok then" and he told me to crouch with my head down and take several deep breaths, gradually getting faster and faster causing me to hyperventilate. I then stood up and he put pressure on my chest and I passed out for 3 seconds. When I recovered I couldn't remember what just happened. People said to me that I hit my head hard on the vending machine and later I got a big bruise from it. When I got home I did some research on this and I found that a lot of people have very bad injuries or even die from it. I read online that there is a 1/3 chance of recovering without any signs of symtoms to this. Basically what it does is cuts off oxygen to your brain and kills some of your brain cells. I don't how bad the bruise is and I know it sounds silly but I am unsure that I will survive.