Well, my sewer has now been de-clogged and my tooth de-pulped. And I am weirdly amused by how fundamentally similar those two procedures actually are.
Anyway, the root canal was long, tedious, uncomfortable and tiring, but not painful (except for the needles at the beginning), and definitely nowhere near the top of the Worst Things I've Experienced in My Life list. And, holy crap, the pain is gone! I'd gotten so used to it that now every time I pull air past that tooth or take a drink of cold water, I feel genuinely shocked that it doesn't hurt. Mind you, my poor jaw definitely feels like it's been held open with clamps for three hours. But I'm sure that will pass.
The sewer problem, by the way, turned out to be due to roots. It seems that at some point I really ought to have the old iron pipes replaced with PVC, otherwise they're likely to cause more problems down the road, but for now I can flush my toilet with impunity again, and all is well. Whew!