Eh not necessarily. If the floatation system fails you might slowly suffocate at the bottom of the sea.
The majority of any given point in the world’s oceans are deeper than the crush depth of any submarine. Submersibles, not so much (modulo Oceangate’s).
Unless you're over deep enough ocean to be crushed.
I don't know what's worse: a gradual realisation that there's going to be nothing that anyone can do to prevent your sudden, violent death or a gradual realisation that you're going to be slowly asphyxiated.
Especially if your government refuses offers to help https://en.wikipedia.org/wiki/Kursk_submarine_disaster