HI
There is nothing to worry about at all. I had my boy neutered on Wed, when we got him home, he was just like his old self, he tucked into his food, he was bouncing all over the place, he was running up and down his ladder, like nothing had happened, he was crawling all over me, like he normally does, he was just glad to be home.
I had my girl neutered the same day, she was the opposite poor little thing, we had to give her pain killers a couple of times, that the vet supplied, she has started eating and tucking into her food again, she is much brighter now, back to her old self again. Its such an awful worry and you really hate to see them in pain and suffering, its awful. I really felt, for my little baby.