it's pressure to the sides of the neck, constricting the blood flow to the brain. Will make you go nighty night in about 3 to 5 seconds. I was put to sleep with a carotid choke once on a take down. It was a baseball bat choke. The guy took me down and I was out before I hit the mat. It was that fast.
Oh blinking hell, would you please stop blinding me with BJJ terminology Please. 3 - 5 seconds, that sounds like impossible to me. That quick would suggest a neck break.