Depression describes clinical sadness not necessarily related to life stresses, believed to be chemically induced in the brain. Depressed patients often have difficulty performing even the simplest of tasks and only want to lie in bed. Chronic pain is often accompanied by depression. Sometimes depressed patients will go through cycles of unusual energy spurts. These are called manic phases. When a patient has both manic and depressive phases, this is called bipolar illness. Depression in a patient with chronic pain makes the treatment program far more difficult. Antidepressant agents are sometimes used to help treat patients with chronic pain and depression.