A disorder in which the memory fails with no known organic cause. Can occur spontaneously for a few hours or days (known as global dissociative amnesia), or after a traumatic event (situation-specific dissociative amnesia). Dissociative amnesia is also known as psychogenic amnesia.
This happens because of severe trauma/stress and is quite interesting because the entire continuity of the memories that are normally in the person’s brain is warped into a new way of thinking because of an extreme inner conflict. The person simply cannot accept that something has happened, so they dissociate.
Fournier, G. (2010). Dissociative Amnesia. Psych Central. Retrieved on July 7, 2015, from http://psychcentral.com/encyclopedia/2008/dissociative-amnesia/