It was not clear (to me) that you were experiencing hypoxia which lead to diminished hearing. Thanks for the clarification, and I retract my snark.
Good story, here’s my only close one:
I used to have a lot to do with LN2, which we used to cool detectors (GeLi - Lithium-drifted Germanium) and vacuum cooling traps for experiments at our university heavy ion accelerator.
We had a room which had a line to a tap from an outside 50,000 liter LN2 tank for filling 20 liter dewars - our group in the building was not the only one to use LN2, but we used a *lot*.
Anyway, about a year after I left the physics institute for self-employment, one of the young graduate students was found frozen stiff (-196 °C is about as stiff as it gets) in that room one morning.
The ventilation system was good enough, so how that came about remains sketchy to me... Though the whole setup was a bit basic - when the dewar was filled there was no automatic shutoff, it would spill over and form clouds on the floor. You’d think PhD candidates were smart enough to close the tap... Anyway, to close up on the oxygen displacement, if someone wanted to go, nitrogen asphyxiation is a pretty good choice.
You sure got my attention with your story. That was horrible. Was it possible that not being diligent about closing the tap, would the tap freeze open?