Like you get transported into an alternate universe where everything is almost same, but with tiny differences. The world looks normal to everyone and you’re the only one that have memories of the differences.
Do you think you would trust your memories or would you think you lost your mind?
I would look for psychiatric help and go over memories of that person with other people. I’d probably wonder if they were real or would also disappear.
Edit: oh shit i just remembered that i confuse things that happened in dreams with real life things sometimes. maybe this would be a more extreme version of that? dreaming a whole person. wow