Recently I had a thought, that if you copied the contents of your brain onto an object that can the simulate it, or even a new brain, then the "new instance" of you will probably just think it's the real you, just that it's on a computer/in a different body now. If New You sees a picture of a partner that left you, or a pet that died when you were a child, it will feel the same sadness you would. And it would just go about the day like you would, with your internal thoughts, because what else would it do?

I think the way I see it now is, your mind is a black box to your current consciousness (with some interfaces to recall things), if you replaced this black box with a perfect simulation, your consciousness might not even notice it. Of course your consciouness has also been programmed since the day you were born, but wouldn't a perfect copy of your mind also copy the current consciouness? Either of you would wake up and think "Ah, I'm brap, and I'm currently in my bed, and yesterday I did x and felt y, and the day before... [iterate until there's nothing else to remember]."

If Original You remains alive, it does get weird, both of you will think "There's someone else with my own exact brain and memory, but I can't feel what s/he's currently feeling!".

There's an Apple movie that explores about what I've written, although I haven't watched it: https://www.hollywoodreporter.com/movies/movie-news/mahersha...