I went through something very similar with my cat Ripley just last Oct. He spent eight days at the vet and then I had to take him back for antibiotic injections for four more days all due to a serious infection. It took him almost two months to get back to his normal behavior (he was 10 1/2 years old at the time). Anyway, the vet said his behavior change was normal and not to worry but it was a long two months getting him back to his old self.

As long as he is doing okay physically I would not worry and just give him some time to fully recover from the experience. Give him lots of extra TLC so he will feel reassured that everything is okay.