What would make someones personality and life change - Amnesia?

I'm writing a book (just for fun) about someone, who has an accident and when they wake up their personality changes and the person he is married too, he doesn't love anymore, etc.

But i want to know something that would changes someones mind like that. Things like Amnesia ?What would make someones personality and life change - Amnesia?
Not amnesia--the amnesia you see in movies really isn't real and is losing popularity in film because it's so fake. However, look into 'dissociative fugue'---that sounds exactly like what you are looking for ;)

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