That is not only permabear speak, but UBER permabear speak. Stocks are not undervalued or overvalued EVER, and if you think so, then you are just trying to add intelligence or study where none belongs. Yes, I know that experts say that stocks are undervalued or overvalued all the time, but that's BS. Stocks are worth on a specific day what someone will pay for them, and that price goes up or down every day. Your comment then that the next decade may not be kind (at least you said MAY) is also just permabear speak. You have ZERO basis for saying that. Monkeys MAY fly out of my butt. There is NOTHING that indicates that stocks will do anything over the next decade that they haven't done historically, and even if you point to something, that's so bogus as nothing could predict today how stocks will do over the next decade. I'm sorry you did not set yourself up to not be worried about such things.
What you SHOULD have done is this:
1) Began investing in diversified STOCK mutual funds as soon as you had a regular job. This should have been an unrelenting practice no matter what the stock market was doing. Pour money in. Pour money in. Pour money in. When the market goes up, great. When the market is down, stocks are just on sale.
2) Along with investing (at least 15% of your income), you should have done all you could to knock out any debt you had as quickly as possible.
3) Once the debt was gone (and even before if you could handle it if perhaps you still had a mortgage), you should have invested MORE than 15%...either in retirement accounts or also non-retirement accounts if necessary).
That's it. Then you wouldn't be worried about how the market does this year or in the next decade.
I know you are retired now, but for anyone who is still making an income and is worried about how the stock market will do in the next decade (or even just to have a very good safety net), one thing to do is to save up as much as 3 YEARS of expenses in cash that you could use to pay bills if the market tanked, giving you time to allow the market to recover...because it will. This money could go in a savings account (even a high yield savings account) or a checking account. The idea isn't to make money on that money...it's just a large emergency fund.