"The presence of two or more distinct identities or personality states," is something you"d expect to hear as the title to an X-files episode. In reality, this line is found in the DSM-IV as a physiological disorder. This rare disorder is called Dissociative Identity Disorder (DID) or formally known as multiple personality disorder. Dissociation is a mental process, which produces a lack of connection in a person's thoughts, memories, feelings, actions, or sense of identity. In DID at least two of the identities or personality states recurrently take control of the person's behavior. In some cases the personalities are so separate that they don't know they inhabit a body with other "people." .
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The origins of dissociative identity disorder are still not understood. Although it's not understood, one theory suggests that it developed in response to childhood abuse. The abuse then can lead to many symptoms in adulthood. Questions have been raised as to why DID occurs and the symptoms that follow it. Because of this uncertainty, misdiagnosis occurs and makes it very difficult to find the correct kind of treatment. Research shows that DID may affect 1% of the general population. .
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Physical and sexual abuse are just examples of two traumatic situations from which a child may resort to "going away" in his or her own head. This ability is typically used as an extremely effective defense against physical and emotional pain. By this dissociative process, thoughts, feelings, memories, and perceptions of the traumatic experiences can be separated off psychologically, allowing the child to function as if trauma had not occurred. DID is said to be a highly creative survival technique, because it allows people in "hopeless" situations to preserve some area of healthy functioning. Overtime, a child who has repeatedly been physically and sexually assaulted "going away" may start to be conditioned and reinforced.