That's awful, but perhaps better than stuck for hours or days inside of a dead, dark, cold submarine at the bottom of the ocean as the oxygen slowly runs out.
Indeed it would. The CO2 would trigger the breathing reflex and panic. Hypoxia does not trigger that and you start to lose yourself, similar to being drunk.
I think the problem is more being stuck in a dark small and cramped space with 4 other people for 96 hours, where there is no on-board toilet and you just don't know if help will arrive in time or not.
Compared to that, I think an instant death due to implosion sounds preferrable.
That is what happens. Confined spaces that have little oxygen are extremely dangerous and have had quite a few deaths because of them. Those who are working in them literally just feel dizzy and confused, fall asleep and die from the lack of oxygen.
There’s about 100 deaths per year in the U.S.
Sometimes even rescuers die because they don’t know about it as well. They try to rescue, get confused and die.
Hypoxia is a terrifying thing.