Major depression is a serious mental health condition that affects a person's mood, thoughts, and behavior. It involves emotional symptoms like feeling sad or empty, loss of interest in activities, feelings of worthlessness, and pessimism. It can also cause changes in behavior, such as changes in appetite, sleep disturbances, and decreased energy. In addition, it affects cognitive abilities like concentration and decision-making and can cause physical symptoms like headaches, digestive problems, and chronic pain. These changes can disrupt a person's ordinary functioning and quality of life.