According to the Mayo Clinic:
“Depression is a medical illness that causes a persistent feeling of sadness and loss of interest. Depression can cause physical symptoms, too.
Also called major depression, major depressive disorder and clinical depression, it affects how you feel, think, and behave. Depression can lead to a variety of emotional and physical problems. You may have trouble doing normal day-to-day activities, and depression may make you feel as if life isn’t worth living.
More than just a bout of the blues, depression isn’t a weakness, nor is it something that you can simply “snap out” of. Depression is a chronic illness that usually requires long-term treatment, like diabetes or high blood pressure. But don’t get discouraged. Most people with depression feel better with medication, psychological counseling or other treatment.”