[Help] My dog has suddenly become much calmer

I have a male pit mix, maybe three years old (we found him). Neutered. Great guy.Usually, when I get home, he wiggles ferociously and kind of hops a bit. He also loves chasing his kong ball and will tear around the yard looking for it.In the past week, he has massively calmed down. He walks instead of runs. I can't see a limp, though. If I throw the ball, he'll jog after it. And he still greets me, but with a wagging tail instead of the joyful spasms he usually has.He is sleeping the same and eating the same. He seems more interested in belly rubs and head pats.is this something to just watch or take to the vet? I can't think of what symptoms to describe other than he suddenly became chill. via /r/dogs http://ift.tt/2qZlcHV