I've been choked out once by a Domme but it wasn't actually in a session. Instead it was on a film set when I was trying to get her off her butt to shoot the next scene. She just decided to teach me a lesson and just walked up behind me, threw me in a chokehold and took me down in front of the other people there. It was a totally non-consensual act but I also gave into it rather than fighting once I realized what was happening.

However, she absolutely knew what she was doing. For myself, I actually was taught how to properly do a chokehold by a friend of mine who is a black belt in some form of Karate (I don't know which it was) and fought in MMA tournaments. The key to safety in a chokehold really has less to do with losing consciousness than making sure it is a proper hold applied in the proper way and is released as soon as you either tap out or drop off.

No matter what, it is definitely edge play but the real risk is that many people don't know what they are doing and will mistakenly arm bar across the front of the neck (you see this in movies ALL THE TIME). This technique can do serious damage to the trachea while they try to cut off your airway (which also takes a long time to do). However, a proper hold actually has zero pressure on the front of the neck and instead is focused on cutting off the blood supply (and oxygen it carries) on the sides/back of your neck.

Chances are if you are starting to lose consciousness in a matter of seconds, that Domme/wrestler was doing it right. But, knowing that someone really knows how to apply a chokehold before consenting to that being ok should be safety concern #1. As for my own experience, there were no after effects and I was totally fine 5 minutes after it happened (other than being pissed).