I had a retirement scare because I retired in April, 2007 at age 41. I can't remember exactly, but my portfolio was down something like 40% at one point in early 2009.
But it did help me learn about myself. I never gave up faith in the portfolio and continued rebalancing and being optimistic until the very end (in March, 2009, on an investment board, someone even made a comment that everyone seems to have no hope except for optimistic Kramer). And even at the nadir I also realized that I was still living on less than 4% of what was left and that it was at least sustainable. I tried to think through my retirement up to that point and didn't have regrets about quitting the job in 2007. I never had thoughts of returning to work (and it probably wasn't even possible during the depths of the recession).
But I could have really messed up by panicking and selling everything.