If your dog is sad or depressed, there are many things you can do to try to boost your dog's spirit. A sad dog can often be uplifted by attention and exercise, but if they appear listless, a small change in their diet may help them out.
As your dog does through their sad transition, which is typically brought on by a sudden change in the dog's life such as a family member passing or moving away, a new home, or even losing another pet that was a favored playmate, they can become less interested in food. In these instances, it's important to get your dog to eat or drink, even if it means giving them foods that you normally don't feed them.
Boiled chicken breasts, hamburger (fat drained, no spices), oatmeal, and even brown rice are filling and tasty meals that should help entice your dog to eat. If they are having trouble drinking as well, add a homemade chicken or beef broth (no salt or spices added) to their water to get them to drink.
If your dog remains sad for more than a week or is losing weight rapidly, see your vet. They can give your dog supplements or shots that can help boost their energy and get them back on the mend. If your dog will not drink for more than 2 days, see your vet for assistance right away.