DID occurs as a result of complex, severe trauma in early childhood. The brain protects the individual by fragmenting the memories, emotions, thoughts and physical sensations into separate identities. This is why it is common for survivors of abuse to only have part of the narrative and not the whole picture, due to different identities taking care of those aspects.
Usually someone can function at a high level through life with minimal issues or awareness of DID, until a major stress triggers an un-doing and the parts come to the surface. Some people come to realise they have DID when they access therapy and parts present to the therapist.
It is a complex condition and someone can have many, multiple parts. Each part has a different role that helps the person – so the part thinks! However, due to the nature of the abuse, the parts often think dying is a form of protection, a way out. This is why incidents of suicide attempts and self-harm behaviours are common for people with DID.
There is an amazing website that has many resources that can help people who have DID or another type of dissociative disorder, resources can also help carers, family members, friends and health professions. Please see PODS (positive outcomes for dissociate survivors) and First Person Plural for more information.