After several days of visiting the vet and receiving fluids subcutaneously, Inky is up and about. He has an appetite and has even begged for treats.
He's still a bit weak -- but still tries to jump on the counter -- and thin. But he's showing some of his old fire. There's a spark in his eyes that wasn't there last week, and he was waiting by the door this morning for his breakfast.
I'll keep my fingers crossed and hope for the best.