People undergoing chronic life stress may find themselves slipping into a depressed mood more and more often. A situational crisis can result in the development of a serious mood disorder. Anxiety, sleep deprivation and poor coping habits such as drug or alcohol use can contribute to feelings of depression.
Major depressive disorder occurs when depression is unrelenting and lasts for an extended period of time (several months). It often includes symptoms of sleep disturbance, appetite and weight changes, feelings of worthlessness, hopelessness, fatigue, apathy, guilt, difficulty concentrating, difficulty completing activities of daily living or working, and suicidal or homicidal thoughts.