I won the 5k!
Okay, not really, but I ran the whole thing (by which I mean I didn't have to stop and walk) and came in firmly in the middle. Results haven't been posted yet, so I don't know exactly where I placed within the mass of about 2000 runners.
I'm just pleased with myself for doing it.
Also, I don't feel anywhere near as bad as I thought I would. Now I want a nap.