This is a horrible thing that children are doing to themselves. They are doing it for the rush. Every parent should sit down with their kids today and tell them how dangerous this activity is and how it can easily kill them.
I am 56 years old and when I was that age we use to do the same thing, except in a safer way.
I never knew of anyone getting hurt or dying from it.
I would take 3 deep breaths and a person behind me would squeeze me around the center of my torso, until I went limp. They would then lie me down. After 5 seconds or so you would wake up.
It was stupid back then. But they must be squeezing around their necks today. Much more dangerous.