Hello,
Dissociative identity disorder is a mental condition that is often confused with attention deficient 
hyperactivity disorder. It is caused mainly due to some type of childhood trauma like death of a near or dear one, physical or sexual abuse. Other conditions that can cause it are natural disasters or 
substance abuse. It is a rare disorder.
Certain factors like stress, substance abuse, drugs, alcohol, etc., can trigger the symptoms. People with DID are suggested to stay away from addictions if any. People suffering from Dissociative identity disorder have one core identity and that is the person's actual / usual personality. He / She may have many alter in their personality due to triggers or 
hallucinations that are not real.
No, the two personalities generally don't fight with one another, don't conflict as such but may produce a gap in memory and other problems that causes them to suffer like temporary 
memory loss, delusions or depression. Various types of 
psychotherapy can help people manage the symptoms of DID. 
Psychotherapy works well provided the person with DID communicate openly and honestly with the people in the support system, during group 
counselling and are not afraid to ask for help when they need. Some also go for 
hypnotherapy but I don't recommend it as Psychotherapy is enough to help DID patients to manage their behaviors and reduce the frequency of identity 'switches'.
Take care. Hope I have answered your question. Let me know if I can assist you further.
Regards,
Dr. Nupur K., General & Family Physician