Depression is widely thought of as a mood disorder based in the brain, but it is in fact a whole-body disorder. Lethargy, for example, is a common sign of depression that robs people of the will to move. But the links between depression and the body are more than just psychological. Depression has effects on body metabolism that limit available mental and physical energy. Depression negatively affects almost every system of the body. It disrupts sleep, affects appetite, alters the perception of pain, and weakens immunity—in addition to darkening your thinking and your outlook so that you can’t envision a brighter future ahead. Depression is so much a body disorder that experts believe that the vast majority of cases show up in doctors’ offices expressed primarily in physical symptoms such a chronic pain and fatigue.