Ship of theseus and continuity of death.
Continuity of death. You are alive when you exist. You are dead when you don't. I think it's useful to think that a fraction of you can exist. Consider the 5 year old me. I am a very different person now and have very few memories remaining from that time. A large fraction of that 5 year old no longer exists. But some of it is still part of me. The graph of a fraction of present me that existed and will exist may be modeled as a gaussian, where the horizontal axis is time, centered on present (clamped by the beginnin...
The multiverse might be very big. Perhaps if you're mad enough having the disease will bring you to a state of mind that a version with no disease has. That's why wizards have to be mad to use magic.