Depression is a condition that impacts the body, emotions, and thoughts, influencing how an individual eats, sleeps, perceives themselves, and views the world. Unlike a temporary feeling of sadness, depression is not a sign of personal frailty nor something that can simply be overcome by willpower. Individuals with depression cannot just 'snap out of it.' Without intervention, the symptoms may persist for an extended period—weeks, months, or even years. Nonetheless, most people with depression can improve significantly with the right treatment. Symptoms of depression include a diminished interest in once-enjoyed activities, including sex; changes in appetite leading to weight loss or gain; a lack of emotional expression; a continual feeling of sadness, anxiety, or emptiness; feelings of hopelessness, pessimism, guilt, worthlessness, or helplessness; withdrawal from social interactions; extreme fatigue, low energy, and a sense of sluggishness; disturbances in sleep patterns, such as insomnia, waking up too early, or excessive sleeping; difficulties with concentration, memory, or decision-making; unusual restlessness or irritability; ongoing physical issues like headaches, digestive problems, or persistent pain that do not improve with treatment; and thoughts of death, suicide, or attempts at suicide. The main categories of depression include major depressive disorder, dysthymia, and bipolar disorder, also known as manic-depressive illness.