Fugue state

A fugue state was, according to the Tenth Doctor, "where the mind just runs away because it can't bear to look back."

Jackson Lake suffered from such a state when he lost his wife and son to the Cybermen. While entering a fugue state, he saw an infostamp containing information on the Doctor, which he used to drive off the Cybermen. The infostamp backfired and transmitted all its information into Lake's mind, and he began to think that he was the Doctor. (TV: The Next Doctor)