Dissociative Identity Disorder (DID) is a severe condition in which two or more distinct identities, or personality states, alternately take control of an individual. Brain imaging studies have corroborated identity transitions in many patients. These are not demonic entities but identities created from trauma or abuse as a child. It is a recognized condition in the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR, section 300.14)
The treatment for DID is going to a Christian Counselor and each alter is recognized, the issues of each alter are resolved, and allow Jesus as the Great Physician to heal the pain.