According to this article from the Centers for Disease Control and Prevention, depression is not just having "the blues" or the emotions we feel when grieving the loss of a loved one. It is a true medical condition that is treatable, like diabetes or hypertension.
It is not unusual for caregivers to develop mild or more serious depression as a result of the constant demands they face in providing care. According to the Family Caregiver Alliance, early attention to symptoms of depression through exercise, a healthy diet or positive support of family and friends may help to prevent the development of a more serious depression over time.
To achieve its mission of transforming the understanding and treatment of mental illness, the National Institute of Mental Health website provides a variety of resources to help you better understand all facets of depression.