A lack of energy or enthusiasm. Loss of appetite or a decrease in food and water intake. Sleeping more than usual or a lack of interest in play or exercise. Changes in behavior, such as becoming more clingy or withdrawing from social interaction. A change in body posture, such as slumping or a loss of muscle tone. A change in vocalization, such as a lack of barking or a change in the pitch of the bark. Hre you can download free sad dog pic.