Thanks for the response, Lynn!

He seems to be doing a little better. His throat swelling went away yesterday, but he is pretty lethargic, not eating. Yes, hanging out in the water. I was up about six times last night with my infant, and each time I peeked at him he was in a different place --- looked like he'd stay in the water for a bit, climb out and under some leaf litter, and then he'd be back in the water again the next time I got up.

Still alive this morning, so after my midnight googling, went out early and found the ingredients for amphibian ringer's solution. Gave him a good soak for an hour this morning, and it seems to have helped a bit -- he seems much more alert.

I did notice two things: a teeeeeeny bug running across him when I placed him in the solution (a mite?), and what almost looks like flaky skin on his belly. I only noticed the skin as it turned whiteish. No open sores or anything, no abrasions or visible injury -- maybe skin getting ready to shed? Any advice would be much appreciated. Off to google this!

He's in a glass/latex/screen tank, with moss and coconut substrate, mopani wood, one fake plant, three real plants that have provided some natural leaf litter.
He's been the most active and sociable of the frogs...so sad to seem him ill.

I'll try to get a picture when I soak him again, and will keep you updated.