If the many worlds of the Many Worlds Interpretation of quantum mechanics are real, there's at least a good chance that Quantum Immortality is real as well: All conscious beings should expect to experience the next moment in at least one Everett branch even if they stop existing in all other branches, and the moment after that in at least one other branch, and so on forever.
However, the transition from life to death isn't usually a binary change. For most people it happens slowly as your brain and the rest of your body deteriorates, often painfully.
Doesn't it follow that each of us should expect to keep living in this state of constant degradation and suffering for a very, very long time, perhaps forever?
I don't know much about quantum mechanics, so I don't have anything to contribute to this discussion. I'm just terrified, and I'd like, not to be reassured by well-meaning lies, but to know the truth. How likely is it that Quantum Torment is real?
The more conventional perspective on QM is of a single nondeterministic world or of a single world in which events have subquantum causes. From this perspective "quantum torment" - lingering indefinitely in a near-death state - is logically possible but inconceivably improbable, something that wouldn't happen even if you reran the history of the cosmos a googol times, because it involves the quantum dice (whether deterministic or nondeterministic) repeatedly coming up just the right way to prevent your body from finally giving up the ghost.
In a many-worlds theory all logical possibilities are supposed to happen, but the empirically validated probabilities still have to be respected. That is, we don't see all possible events occurring with equal probability, we see them occurring with probabilities given by the Born rule of QM. How to justify this within MWI is a major problem, one of several that the theory faces. But assuming that it is resolved, then the frequency with which quantum torment is realized in the multiverse must be the same as the probability with which it is expected in single-world QM, i.e. it represents a vanishingly small fraction of worlds. In the vast, vast majority of worlds you just die.
If someone is an "identity freak", they need to condition the distribution on "person X is alive" (where "X" -- the person of interest). And now the question is whether the average health deteriorates "as time goes to infinity" -- it probably deteriorates to some minimum livable floor and then bounces up once we cross singularity. (I'm not an "identity freak" BTW.)