Our FreeBSD server suddenly rebooted itself and we didn't have notes on exactly what to do in that case*. Unfortunately for you all, I was the only HN sysadmin around—there exist other, much better ones—and it took me a while to figure out the sequence. Then a helpful colleague asked a good question that triggered the right memory in my brain, and poof we were back up.
* (since some of you are about to ask—yes, we do now)
* (since some of you are about to ask—yes, we do now)