Booted up my Fedora box at work this morning but instead of starting normally it put me in emergency mode with a message to check the logs. On the whole I'm very pleased with this development. It gave me a prompt to give it the root password and then I could view the logs with journalctl from there.
Unfortunately though the resolution of the text was such that I couldn't read most of it - it went off the screen. So that's a bit of a problem. I had the system start up to the default state and then I was able to look at the logs in Konsole - which was a lot nicer. Looks like the hard drive is on its way out the door.
I ran smartmon and double checked. So now I'm copying everything off that I might be worried about. (In addition to my normal backups. I like to do this just in case.) And I think I've found the Western Digital drive that I'll be buying to replace this Seagate drive that is toast.
From what I've read WD is much more reliable than Seagate. Though I can't complain. It is the original drive that came with the machine and I bought in 2010. I don't think 4 years is an impressive time for a drive to last but I don't think it is terrible either.
But kudos to Fedora for alerting me to the problem and giving me time to plan ahead. The system still seems to run fine, I'm typing this JE from it - but I know that this wont stay true. And probably I could route around the damage for a while but I'd rather not. Storage is too cheap nowadays. I'll be picking up another TB drive for about $50.