OK, so I thought I'd do a "good news" post :).
1. I've been more or less steadily recovering for around 3 weeks. My walking has gone from around the house to around the block to a 20-minute walk in the morning. My feet are still tingly/painful, and my back/hips are stiff and weird-feeling (and I still have some odd nerve sensations in various places), but it's much more manageable, and I can do the basic things of life (and actually enjoy them). Yay!
2. I'm sleeping *somewhat* better, which might be related to this. I've gone from maybe 4 hours a night (my average from April through June) to a little over 4.5 hours of sleep. I'm using sleepio.com (it seems connected to Britain's NHS?) to do online CBT-I, if any of you insomniacs are interested in trying it with me. I'd someday love to sleep 6 hours :).
3. I talked to a spine specialist today, and they told me what I guessed: I have some pretty generic spine issues for my age: a bit of arthritis here, some bulging discs there, but no "red" flags (and no sign of cancer). My blood markers--thyroid, inflammation, potassium, calcium, etc.--all seemed normal. The specialist mentioned the possibility of a nerve getting bothered by some movement I didn't even notice, or perhaps some lingering side-effect from chemo all those years ago (the feet bit, especially), and the sleep issue possibly being related to fibromyalgia-ish symptoms. The fact that I wasn't in extreme pain means that none of this especially matters to the next step: going back to PT and trying again.
4. In the end, I'm pretty happy/optimistic that things seem to be (slowly) getting better, but am still a bit skittish about not knowing what exactly caused the whole "I can't walk" thing. (I'd prefer to avoid a repeat...).
In any case, this should be my last post for a while (hopefully). Thanks again for all the support!
Brendan