I have a 3 year old blue heeler cross border collie dog. He sleeps an awful lot despite being able to run around and enjoying play time. Most of the time he just sits his arse down on the sofa. I make sure he gets a fair bit of exercise a day, with long walks, and having a run around and playing fetch and the like but he doesn't seem to want to explore around the house or chew his toys at all he just curls up on the sofa, for hours unless i play with him. He won't do anything active of his own accord unless i'm there. Is he a lazy dog and if so how can i fix this????