Depression affects people in different ways. Some people feel sad and have a "flat" affect. One of the most common symptoms of depression is agitation and anger. Many people do not realize that anger may be a symptom of depression. Common symptoms of depression include sleep disturbance, restlessness, irritability, low energy level, and anhedonia (loss of interest in activites that are normally pleasurable). Many people have appetite disturbance or irregular appetite, weight loss or weight gain. When a person suffers with depression, he or she may often feel overwhelmed and have difficulty concentrating.