Didn't your vet say to confine him for a few days because of the pain? My Simon wasn't up to running around but your kitty may still be swollen from the surgery.

I know Simon was in pain when I finally let him have free range of the house. He went up and down the steps too many times and that night couldn't put his legs together. He laid on the bed with one leg in the air. Poor baby. I had to prop his leg on a pillow.

Is your kitty showing any signs of the operation?