Dogs will hide pain and injury. In the wild, injured animals will be attacked and killed, and our dogs still have the protective instincts to hide pain from view.
Watch your dog closely to notice physical problems. Sometimes the only indication of a problem is a change in behavior, refusal to climb the stairs or jump onto furniture.
Refusal to eat, walking slowly or lack of energy, sleeping more than usual, head shaking and licking, sleeping in a different posture or a different place are all potential signs of serious illness.
To catch problems early be sure to watch your dog for signs of new, different, or changing behaviors.