Civilization might collapse; I might get hit by a bus; or I might just claw through some of my biases but not others, make poor choices, and fail to accomplish much of anything.

If those things are true, then you were already enduring the possibility. Admitting it doesn't make it worse.

Rationality has stripped me of some of my traditional sources of confidence that everything will work out OK, but it hasn't provided any new ones -- there is no formula that I can recite to myself to say "Well, as long as I do this, then everything will be fine."

What do you need that confidence for?

In the last day or two, it's occurred to me that nearly all I have ever done in my life is try to solve problems and find the "right" answers, and one particularly perplexing puzzle I've been trying to solve, cannot be answered "correctly". It can only be answered by an essentially arbitrary choice on my part - a choice of what I want the answer to be.

One would think that this would be easy, then, but the catch is that to be "right", the choice has to be a choice, not an attempt to divine an optimal answer -- one that brings me the most pain or least pleasure. In a certain sense, if I cannot choose arbitrarily, then I have made no choice at all, and no real progress has been made.

I think there is a certain similarity between your problem and mine, and it is this:

Freedom isn't easy, if you've been been practicing all your life to be a slave.

And it doesn't even matter that much what it is you were practicing being a slave to.