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Final Approach
Of course, with most of those, it would be unsafe to drive as well. Exceptions would be those involving sensitivity to rapid pressure changes, and rapid but gradual incapacitation where one would have time to pull over to the side of the road. But I suspect those are a tiny minority of all conditions that would truly affect safety of flight.There are some medical issues that are serious enough that it would obviously be unsafe to fly anything. There are others where that is not the case.
(I'm not counting conditions involving impairment at altitude. Those are relatively common, but the altitude factor can usually be avoided by not flying so high.)