Chronic pain (usually pain lasting for over 12 weeks) may arise from an initial injury, such as a back sprain, or there may be an ongoing cause, such as an illness. There may also be no clear cause. Other health problems, such as fatigue, sleep disturbance, decreased appetite, and mood changes, often accompany and effect pain and a person’s capabilities to manage it. Pain management physicians are tertiary specialists with particular expertise in this area of medicine.