Depression (also known as major depression or major depressive disorder) is a psychiatric disorder that affects mood, behavior, and overall health. It causes prolonged feelings of sadness, emptiness, or hopelessness, and a loss of interest in activities that were once enjoyed. People with depression may also have changes in appetite (leading to overeating or not eating enough), changes in sleeping patterns (sleeping too much or not being able to sleep), loss of energy, and difficulty concentrating. Although depression is considered primarily a mental health disorder, it can also have physical features including headaches, other unexplained aches and pains, unusually slow or fast movements, and digestive problems. To be diagnosed with depression, an individual must have signs and symptoms nearly every day for at least 2 weeks. However, the features of this condition vary widely.