An old dog can develop hyperactivity from his glands that produce adrenaline. A common symptom of this hyperactivity is the loss of hair. Old dogs can contract diabetes, especially femalold dog illinessese dogs. The symptoms are similar to the ones on humans: general fatigue, thirstiness and vomiting. Make sure you watch out for these symptoms and run to the veterinarian to make an analysis if they show up. Unfortunately, pills that reduce the sugar level on the blood of your diabetic dog do not exist. You must learn how to give insulin injections to your dog.  Probably this will be difficult at first, and you will be afraid to do it, but if your dog really is diabetic, you have no other choice then to try your best and give your dog his injection. If the disease is diagnosed and treated in time, your dog will be able to live a couple of years happily.