Everything stopped at once, which is always the tell. Not "the NAS is slow", not "this one site is down", but the whole house going dark: phones spinning, the telly refusing to load, my partner appearing in the doorway with The Look. When it all breaks together, it's DNS, and when it's DNS it's usually me.
I run Pi-hole at home, forwarding upstream to a local Unbound resolver. Sensible enough. Except that morning I'd "tidied up" the Unbound config and, without quite meaning to, pointed its upstream back at the Pi-hole. So Pi-hole asked Unbound, Unbound asked Pi-hole, and the two of them sat there politely deferring to each other until every query timed out. A textbook loop, built by hand, by me.
The fix took thirty seconds once I actually read pihole -t and saw the same queries bouncing. Point Unbound at root hints and the real world again, restart, done. The diagnosis took the better part of an hour because I spent the first forty minutes convinced it was the ISP.
The lesson isn't "don't run your own DNS". It's that there should have been nothing to tidy at half seven in the morning before coffee. The config was already fine. I just couldn't leave it alone.