Okay, hi, update!
It was indeed an RI. We found a very nice vet who was very good with him, and he said that it was a good thing that it was caught early. About a month or so of doses later, and the lil one is doing a lot better. His last shot was a few days ago, and we're both pretty happy to be done with them.
More questions.
He was still drooling a bit after the last dose, which worried me, but since it's been a long weekend, the vet's office was closed. Then yesterday he shed, and now he looks and acts perfectly fine. Would anyone suggest a follow-up visit with the vet just in case, or what?