I am also guessing that he is reacting to the anesthetic. It can do all sorts of weird things. My vet kept Hekitty overnight because she was yowling constantly, and still staggering. It happens. IF he is wearing a cone, just keep an eye on him, and try to keep him quiet. If he is not, try to get one on him! If he is still displaying this behavior in the morning, give your vet a call.