If your dog is not eating or drinking as much as usual, especially if they are losing weight or becoming dehydrated, it is important to consult with a veterinarian. Many common causes of an unappetizing appetite or thirst can be easily rectified with a change in your dog's diet and/or lifestyle habits. However, if your dog exhibits significant behavioral changes such as refusal to eat or becomes excessively reclusive, then you should contact your veterinarian for further evaluation.