This is a technique where the subject takes deep breaths, holds a comfortable 1/2 breath and the helper pinches off gently, his cartorid arteries from behind. You pass out, but still breathing, the martial arts choke off. Then release the arteries, the supercharged, oxygen rich blood, hits the brain and the experience is weird to say the least. But, not un-pleasant.
I was a hippy then and explicitly trusted everyone in the room. I would not try this today, with so-called friends. You are completely helpless and thoughtless. You come to with no Reality. That's what's weird. I remember once I came around, it only takes a few seconds, but :
Without recall of any past or anticipation of future, Reality was very 2D, a white un-focused expanse. New born. And I was on a ocean of waves. That turned out, after a few more seconds of pure wonder, (no fear,) to be the natural joshing and giggling of the crowd holding me up. I had been unaware of even that. They had lifted me up bodily, flat on my back to 1" from the the celling, completely without my knowledge.