Over decades, people have been paying more and more attention to dogs' physical and mental health as they may also suffer from the pain caused by mental illness. According to Dr. Gregory Burn's Research on dog emotions, it shows that the areas of the human brain that are active when experiencing certain emotions are also active in dogs. We can extrapolate from this data that dogs experience similar emotions when these areas are active. When pets are more integrated into our daily lives, they might be affected by people or the environment.
*While depression isn't typically diagnosed in dogs, vets and behaviorists want owners to become more aware of the signs to look out for.