Hey! As someone who loves auto-erotic asphyxiation, let me put in my two cents!

There are 2 main ways you can die. One is obviously asphyxiation. The other is from circulation being cut. This almost happened to me. My partner had her hands around my neck, but she put pressure on the wrong part and I started to black out. Luckily, I was able to smack her shoulder and she got the hint. This second one feels just like passing out, because you are. Black splotches blossom in your vision until they overtake your sight and you're out. It can take as little as 10 seconds for a person to die from this (minimum, usually it takes a little longer but regardless its quick and mostly painless).

But we like the fun stuff yes?

Yes, lack of oxygen does increase the intensity of the orgasm. It's AMAZING. I like to describe it in terms of music. The orgasm hits some high notes that I otherwise could never achieve. There's a sharpness to it that drops into the lower notes in a rounded wave-like fashion. That's me though. I don't know about other people.
The pressure does force your tongue out. Pressure builds in your head and it feels a throbbing as the blood tries to rush through. the Throbbing sounds like a roaring in your ears. Kind of like the rushing sound you hear when you put your ear up to a sea-shell, only pulsing and much louder. You do tend to cry (as in your eyes leak, not from sadness). Your eyes feel under presure so they can bulge but they do feel like they're bugging out even as you close your eyes. Your whole head has this sensation of tension. As blood pressure mounts there is a chance you will get a bloody nose and it will pour out because of the pressure (I've had this happen before).
It ran out my nose and down my neck and chest. Tiny blood vessels in your face burst. When I've had this happen its very minor but leaves you with a sort of blush. Like freckles, only bright red and small enough that most people shouldn't notice in your day-to-day, but it is there.
The pressure does get painful, and true asphyxiation (not auto-erotic) has a whole new set of issues. Once your air supply is cut off your lungs hurt from lack of air and the strain of trying to breath. I haven't gone that far but I've heard your chest feels like it's caving in. It can take 10 minutes for a person to die this way because in the initial panic you tend to take a few deep breaths and your heart rate increases which oxygenates your brain pretty well, lengthening the time it takes for you to die. When you die of asphyxiation its because your brain runs out of oxygen and bleeps out.

Your body also starves of oxygen which is important for your muscles and nervous system as well. As your body starves, your muscles will contract in different places.
Once, I was able to slow my breathing down until I stopped and held it there for nearly five minutes. My arms, legs, and other muscles like my abdominal ones would twitch randomly until I blacked out and my body re-set, getting breathing going again, etc.


Of course, this is a work of fantasy, so it doesn't have to be 100% true to what would actually happen to you in that situation, but you can play with it!