As far as I know, diabetes was ruled out, and I know my mom mentioned Fanconi and took our vet that handy dandy printout for vets, and he seems to think it's a tumor. He has had extensive bloodwork done, and his urine was tested at the vet, all coming out normal.
As for the vision, we haven't noticed a thing with it, and the vet said it could very well me the aftermath of the allergic reaction, and he might have been in a fog. I guess he had laid a treat down to the side of him, and it was obvious that he only found it by scent; he literally just didn't see it. So we will have that checked again after a couple days have gone by and he is feeling better.
I will check on the basenji vet idea…I know my mom loves this new vet we have, and she is really really picky about the care our boy is getting. So even though I don't have all the details quite straight (it changes daily!), I trust her judgement. Thanks all for the support!!
Will post more again later, OH is begging me to come watch 24!