Pain can also arise from a functional disturbance in the nervous system. Chronic pain is defined as pain that overwhelms all other symptoms and may become the problem. It may affect people so that often they cannot work, lose their appetites, and physical activity of any kind is exhausting and aggravates the pain. Chronic pain is considered a major medical condition that can and should be treated accordingly. Chronic pain may have started from an initial illness or accident, from which a person has long since recovered, or there may be an ongoing cause of pain, such as arthritis or cancer.
Many people suffer from chronic pain in the absence of any past injury or evidence of illness.
The most common type of chronic pain is from an abnormal function in the nervous system. Neuropathic pain refers to pain that can arise when there is abnormal function in the peripheral nervous system. This depression and irritability often leads to insomnia and weariness, which compounds the problem by causing more irritability, depression, and pain. The urge to stop the pain can make some people drug dependent, and may drive others to have repeated surgeries, or resort to questionable treatments. Heat and cold treatments can reduce the stiffness and pain, particularly of arthritis.