loss of consciousness from hanging when done right is usually around 5-15s with 20s as a worst-case scenario. your understanding on rope and ligature and knot position is correct. directly under the jaw is often the best place. arbor knot (noose knot + stopper knot) for the ligature and bowline knot, anchor hitch knot, or overhand loop knot for the anchor point, according to a very helpful user's
post.
from what i understand, compressing
only certain veins in the neck cause that head-exploding feeling.
there are veins that purge blood from the brain back to the heart and arteries that bring oxygenated blood to the brain. as a result, when
only the vein is blocked and the artery is left untouched, nothing is allowing the blood to leave and it builds up because of the untouched artery, causing that agonizing, exploding feeling due to an excess of blood in the brain.
the veins, iirc, are much easier to hit than the arteries because the former needs much less force to block than the latter, as well as the depth.
however, with the right rope and its thinness, depth should be no issue as your body weight will help tighten the ligature into the neck and hit those key veins and arteries. hitting those arteries are also what is needed for quick unconsciousness since the brain is very sensitive to oxygen deprivation; take away its source (the key arteries) and brain cells will rapidly die. average time frame for this loss of consciousness is around 5-15s if done right.
as for choking, unfortunately, that's just an unavoidable side-effect. body weight will slide the rope to the highest point on the neck and cause the inner muscles to force the tongue up and block your airway. hyperventilating beforehand can help with this as it lets you hold your breath longer without having that panicky feeling of CO2 build-up arise. additionally, lubricating your rope to help it slide to that highest point is often beneficial and recommended.
source(s):
this much more helpful user's post
hanging mechanics (from the same user)
i hope this helps you and i don't mean to reiterate empty platitudes, but i'm sorry you're suffering this way.
edit: spelling