I agree with lardy. Do you have pet insurance? If you do, I would be tempted to think about asking the vet to do some tests to rule out anything more sinister. I really regret that a few years ago, I didn't cotton on to the signs that one of my dogs became much quieter and sleepier and grumpier when the other dogs tried to get her to play more. She was only about 6-turned out she was really poorly with liver cancer. I so wish we had got her checked out sooner-she was insured with petplan, so we didn't even have to worry about the cost of any tests. Really hope it's nothing serious with your dog CC, but for peace of mind I would always check with the vet sooner rather than later.