my pup is settling down very nicely, he's now 5 months old and gets plenty of exercise, but the thing he does after a long walk is confusing me. I'll take his lead off in the living room and he will go nuts, runs around in circles, jumps on the sofa starts barking at me, this will last around 5 minutes then he will sleep for hours !! is this just the last of his energy getting used up or something else??