According to Bonnie Beaver, DVM, signs your companion may be suffering typically include:
A depressed pet may stop interacting with his friends, including special people and other animals in the home.
They might no longer show any interest in taking walks or playing. He or she might also tend to move slower and with little purpose in their step.
Changes in appetite
Your pet might lose his or her appetite, and this could lead to weight loss. Alternatively, a depressed animal might eat more than usual and begin to gain weight.
Changes in sleep habits
Depressed pets tend to sleep more, but some may become more restless and unable to sleep well. You know them best, and can probably tell when something is a bit "off."