I had a high school friend who I strongly suspect suffered from either schizophrenia or DID. There were times when he would swear he was a soldier, even though he was just a high school student and the closest he came to marching was in band. At first I'd pass it off as a joke or prank, but one day I took a really good look at his eyes when he started wigging out, and it was like seeing a stranger. It sounds crazy but it was a different personality behind those eyes. When he would come back down from it to his normal personality, you could see the change in his expressions. He also claimed he didn't recall his thoughts or actions while he was "the soldier".
Years later, long after we had drifted apart as friends, I found out he murdered his father and tried to kill his mother and brother as well, and went to prison for life.
A second cousin , as a child , her father had cancer at the time, he awoke one night and his little girl was just about to stab him with a big kitchen knife, apparently based on what the family said , his little daughter had no recollection of the drama the night before, she became a totally normal adult with no mental problems.
Years later, long after we had drifted apart as friends, I found out he murdered his father and tried to kill his mother and brother as well, and went to prison for life.