It was long assumed that early played a key role in the development of dissociative identity disorder. however, we now know this has not happened in most cases.

Trauma

Explanation:

Trauma is the psychological-emotional fear that indicated to emotional instability. Trauma is related to rap-e, accidental event, and disaster. After occurring a tragic event person create self-defense like repression of the tragic event that later on developed a psychological disorder such as dissociate identity disorder.

In trauma, a person develops physically as psychological symptoms. Headache, nausea, forgetting are the symptoms that are related to the tragic event.  

Thus in the above statement person develop dissociate identity disorder but in most cases it does not happen.

economic