what if I found out I was a different person than I thought I was theme

It is revealed to someone that their background is very different from what they believed it was.

Examples

In ds93x05 "Second Skin", Kira was told that she is in fact a Cardassian spy who has been mentally conditioned to think herself Bajoran in order to make infiltration more believable.

13 total · 4 choice · 6 major · 2 minor

StoryLevelMotivation
as1985e2x20 choice Not only did Alan find out that he was moving across the galaxy to a planet named Alturus, but soon after he also realized that he was, in fact, not even an Earthling himself.
ds93x05 choice Cardassians concocted elaborate plot to convince Kira she was really an undercover Cardassian agent who had lost all her memories
movie: Megaville (1990) choice While we are led to believe that Palinov had assumed Jensen's identity, it turned out that it was actually Jensen and that he's been implanted with Palinov's memories.
movie: Suspect Device (1995) choice The mild mannered office worker Dan Jericho was dumbfounded upon finding out that he was a nuclear weapon implanted cyborg.
bbf3x04 major monk found out he was a convicted murderer
movie: Cypher (2002) major The hero of the story Morgan Sullivan came to understand that his identity and memories were false, and that he was actually another man named Sebastian Rooks.
rd1988e5x06 major The crew woke up from a virtual reality game to find that they were not who they thought they were.
tz1959e1x34 major Marsha found out that she was actually a department store mannequin come to life for a month.
tz1985e2x04a major Marsha found out that she was actually an escaped mannequin from a local shopping mall.
tz2019e1x08 major Eve was shocked to discover that she was actually a space alien from another dimension.