I have spent many a month in the oceans deep and freezing oceans, but always felt safe, even though knowing the consequences of a tragic event.
Haven't read any details on this tragedy, but assuming the Hull remained intact, the crew would have been exposed to a living hell.
Too deep to escape and every breath taken depleting that available, and as the hrs ticked on, starting to gasp as the oxygen levels fall.
Freezing cold, no doubt pitch black and knowing that when you close your eyes as you drift off to sleep, you will never reopen them.
RIP to them all and godspeed all submariners at sea, a safe return on completion of their respective mission.
Condolences to all their families.
Edit: in my years as a submariner, I only experienced one scare.