Somatoform pain disorder is a mental illness that causes pain. No apparent cause for the pain can be found through medical tests and it is not the result of drug/alcohol abuse or another mental illness. In somatoform pain disorder, your doctor believes that you are not faking your pain. The pain experienced is real, and persistent enough to interfere with your daily life. The disease also causes high levels of stress and frustration about there being no known cause of the pain.