Pain can happen just because the nerves do not work right . This is called neuropathic pain . Pain can be classed according to its location in the body , as in headache , low back pain and pelvic pain ; or according to the body system involved , such as myofascial pain ( emanating from skeletal muscles or the fibrous sheath surrounding them ) , rheumatic pain ( emanating from the joints and surrounding tissue ) , neuropathic pain ( caused by damage or illness affecting the somatosensory system ) , or vascular ( pain from blood vessels ) .