Dissociative disorders are related to trauma and occur when there is a lack of integration and sufficient cohesiveness in the personality. The causes are extreme events that totally overwhelm the person's capacity to integrate or to make meaning out of them. The memories of the disturbing and traumatic events are held in a part or parts of the person's personality separate from the everyday functioning part. The person may switch between the two or more parts of the personality, and when in the part holding the trauma, feel as if they are completely back in time at the time that it took place.
People who have suffered severe neglect and ongoing extreme abuse in childhood, especially if the perpetrators are the parents, are those who are likely to suffer the most complex of dissociative disorders, dissociative identity disorder or DID. Sometimes there is fragmentation of the personality with many parts or alters who take over in different situations. It is a very complex and serious condition, although many sufferers are able to function very well from a specific part of the self. Highly specialised treatment is necessary, and may be lengthy.