“It takes an awful lot of determination to choke yourself when you could easily stand up and relieve the pressure. It takes overcoming the self-preservation instinct not to stand up and relieve the pressure.”
This is just not true. For evidence, just look at the game of “pass out” that teenagers play, where they intentional asphyxiate themselves until they pass out. It is quite easy to overcome this instinct until you are unconsciousness and unable to physically resist.
The only difference between that game and suicide is that in the game, you are in a position where, as soon as you pass out, the pressure is relieved and oxygen starts flowing again, so you don’t (usually) die. If instead, you were in a position where you would need to move in order to restore the oxygen flow, you would likely die without ever regaining consciousness.
Another simple evidence that your contention is wrong is an activity as common as swimming. It’s against your self preservation instinct to dive underwater and hold your breath while your oxygen levels drop, and yet people do this intentionally and casually all the time. The self-preservation instinct might be a high hurdle for lower animals to hop over, but compared to the force of human will, it’s pretty insignificant.
I’m going to disagree with you because everything you just mentioned had an escape clause built into it. They weren’t really risking anything.
We had a drowning in the bathtub murder trial around here not too long ago, and the prosecutor’s point was that even when unconscious a body’s reaction would be to flail out of that water.
So, I’ll stick with my opinion. It takes determination to kill yourself in such a way.