Bad news for suicidal people: death is not an experience within life. You can’t want non-existence because non-existence doesn’t exist. If it did exist, it wouldn’t be non-existence, would it? You cannot actually want to die in the ultimate sense. You can’t want to be outside of your own consciousness, because you wouldn’t be ‘you’ anymore, if you were. You can’t want non-existence. You can only want whatever you’re feeling to stop. You literally cannot escape, there’s no point trying.
Quantum immortality is usually explained in the following way: each time you die, that is, each time your stream of consciousness is irreparably severed, (be it from death or coma or traumatic brain injury) you punch through into a parallel universe where you’re still alive, and you keep doing this forever, such that 10,000 years from now, you will still be alive in some parallel universe in which you’ve somehow been able to survive as a conscious mummy, a freak of nature, like that Sibyl hanging in a jar. 100,000 years, somehow you’re still alive and conscious as basically a desiccated raisin in a wheelchair, a marvel of modern science, a total anomaly. Then somehow you’re still there and conscious long after the last proton decays and the universe has ceased to exist via heat-death, namely by spontaneously re-arranging yourself (or some other substrate capable of bearing your current stream of consciousness) out of emergent fluctuations in the quantum foam as a Boltzmann brain. But that is nonsensical to me, and there’s a much better formulation of the idea that can be made with a few simple amendments.
The premise is the same: I think you just quantum tunnel into the next closest orthogonal universe parallel to the current timeline when you die, and then resume your consciousness in that other universe about a picosecond after the moment you died in this one as if nothing happened. But then an important distinction is introduced: orthogonality, in terms of the spatial proximity of POSSIBLE universes on a branching probability tree conceived as a higher-dimensional structure enfolded in the fifth dimension, from which ‘time’ emerges as a lower 4-th dimensional projection. You just keep branching through universes in the manner described until you get to the furthest possible parallel universe in which you’re still alive, die in that one, and then tunnel all the way back down into the first universe you gained consciousness in, and then re-live your whole branching timeline over and over again from the moment of birth to death throughout the eternities, forever.
In other words, the parallel universe you punch through in order to sustain consciousness has to still be physically possible, and being a 10,000 year old conscious mummy is not possible, so it is simply not part of the branching structure of possible realities you’re moving through. (Similarly, I do not believe that consciousness is a purely computationally reducible phenomenon, so I do not believe Boltzmann brains are possible.) If I get hit by a car walking the street, I would quantum tunnel into the closest parallel branching universe in which I’m still alive and conscious, which would be perhaps the universe where I looked both ways before crossing, it wouldn’t be the universe in which nanomachines were invented by that point and I had been injected with them and made invulnerable to physical damage. That universe, on the branching tree of possible universes, would be extremely far away, so I wouldn’t manage to punch through into that reality until I had traversed perhaps 600 trillion years worth of parallel timelines, if nanomachines are physically possible to create in the first place. But let’s say nanomachines are not created for 1,000 years from now: there’s no way to extend my lifespan by 1,000 years to reach that parallel timeline, which means that no matter how many times I traverse the branching tree, I simply cannot get there. In this case, that reality is not part of my branching tree of possible realities. If they’re created 40 years from now, there are ways I could get there by going through parallel universes, so with enough traversals of my timeline/s, I could and thus do eventually get there, and once immortalized by nanomachines, my branching tree will be extended exponentially, not just in terms of my linear stream of consciousness, my perceived longevity, but extended in all lower dimensions, up to the 4th. So my branching-tree grows in all directions, not just in length, so as to include a bunch of new possibilities (orthogonal timelines) I’d otherwise not have access to.
You quantum tunnel through universes in this way until you reach the furthest POSSIBLE universe in which you’re still alive, and then tunnel back to the start of the branching tree after you die in that one, proceeding to relive the whole branching structure forever. People who live in the era where a technology like nanomachines exist, or who can physically survive from now until they are invented, will have much wider branching trees than someone born outside the horizon of that possibility.