Depressive disorders are more than just feeling sad. They cause intense feelings of hopelessness and apathy that interfere with relationships, pleasure in activities, and overall quality of life. 

Depressive disorders include major depressive disorder, persistent depressive disorder, substance/medication-induced depressive disorder, and premenstrual dysphoric disorder. Any of these can lead to constant fatigue, poor concentration, lost interest in hobbies and activities, sleep disturbances, changes in appetite, and thoughts of death or suicide.

The exact cause of depression is unknown, but it may develop from changes in the brain, lifestyle factors, or genetics. Without treatment, symptoms of depression can last for years and continue to worsen.