Apparently so. I have met one that I can assure you that there were two distinct personalities and they had two different memories. In ancient times, this was seen as demon possession. Today, it is recognized by modern psychiatry as multiple personality disorder. How this occurs baffles many scientists but one of the causes appears to be severe shock of some kind of long repressed desires and denial.
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Some people have Dissociative Personality Disorder where they have multiple personalities that the subconscious creates but the original personality isn't aware of. These personalities are often created in order to help the person deal with some kind of repressed memory from childhood (or at least that is the most typical cause that researchers have found thus far).