Depression — also known as major depressive disorder or clinical depression — is a common but serious mood disorder that can interfere with how people feel, think, and handle daily activities, such as sleeping, eating, or working. Although sadness can be a symptom of depression, it does not characterize the disorder. Symptoms of depression include sad or anxious mood, feelings of hopelessness or guilt, loss of interest in previous hobbies or activities, decreased energy, difficulty concentrating or sleeping, changes in appetite or weight, and persistent physical symptoms.
NIH.
