like TheMadRaven explained there are 2 types, or maybe even 3 types
but the mechanism is not entirely correct.


One thing is simply lack of oxygen which our body does not register almost at all and your brain simply stops working nothing hurts sometimes it can even make you feel better and more euphoric

second, if the inability to remove CO2 while there are no problems with oxygen. This happens when you cannot breathe, Blood saturating with CO2 causes all those panic attacks and probably enhances arousal as well.

And third is cutting off blood supply to the brain what causes an almost instant blackout or terrible weakness


I can hardly imagine how it is possible to strangle someone masking them unable to breathe because trachea is pretty hard and applying that amount of force to squish it flat may break it or cause significant injury also squishing arteries will have a much faster effect.

To suffocate someone for real you probably should close their nose and mouth with some pillow or something similar and then wait for a considerable amount of time until they panic and kick around trying to escape


By the way, it is pretty simple to do yourself if you just lie on the belly and force your head into pillow making it hard to breathe. (it is not that you can't but it requires more effort) I admit that it really increases arousal in the right context. But if you are not in the mood it does nothing at all. Or if you wanst to simulate efefct of strangling just bend head up and result will be prety similar.

But if you are writing fiction there is no nned to be realistic, just write something sexy.