I found that liberating, though. If life is here for a moment or forever, it is best not to let death define it. Just live.
Richard Carrier has a few essays on secular valuation of life; you might want to check those out. Keep striving...
Generalizing improperly from my own experience and that of people I know, it seems to me that it gets easier to accept the idea of death for many people as they age. Hopefully we'll crack the aging thing ASAP, but I wonder how many will die of old age even after aging is more-or-less optional.
While I'm too young to say, I think at the time you are old, your brain would have changed (or degraded) sufficiently enough to handle it with relative ease. That's the only way it makes sense to me when I read about ailing people talking about seeing the exit, the final candle, or whatever.
That aside, I also consider "what happens after you die" to be the ultimate question. Because nobody alive, dumb or smart, knows the answer, and nobody has come back to tell us. It just depends on when you think you are ready to find the answer. Perhaps after you solve the unified field theory everything will converge.
Even if true, not everyone would die after their brain has degraded in this way.
Sleep disorders are quite common in the elderly and I would guess that this is mostly due to a fear of death while asleep.
"Either of these are much more likely than the eternal afterlife of a theistic god..."
What's the difference between these two?
Have any secular individuals here come to terms with their own mortality? I haven't yet, but I sure hope I have a while to figure it out. Right now all I've got is a hope that a singularity will grant immortality. Or that this reality is a computer simulation and we wake up in a bigger computer simulation where we get bored sometimes and choose to spend lifetimes during interesting periods of time.
Either of these are much more likely than the eternal afterlife of a theistic god, but not nearly likely enough to give me any comfort. Dr Roth's lesson on mortality seems to be that death is inevitable, but that doesn't give me any satisfaction, for now.