Our 10 month old Shih Tsu was neutered on Wednesday. We got him back back today (he was with my parents yesterday) and noticed that when he walks slowly, his rear end drags toward the ground, almost as if he is getting ready to go to the bathroom. (The squat isn't that low, but just wanted to use it as an example) Is this common? He also seems lethargic. How long should we expect this to last?