I've only had this happen once and I can't explain it. I'm currently living with my fiancé and I've always had dreams that are "Donnie Themed," which just means I dream about him a lot.
I had one "dream" in which I consciously was looking for him in my dream realm. I found him as a child in a childhood home of his. He was about 6 years old. I was me but I know I didn't look like myself.
I walked into his bedroom and sat on his bed and proceeded to play Nintendo game's with him. I was a good number of years older than him, I know this because I was taller than him. As we're playing the games I tell him he doesn't know me yet, but he will. I tell him I love him very much and that he will eventually spend his life with me.
At the end of the video game, the dream ends. I wake up and tell him I had a strange dream about him and start describing the dream I just described here. He stops me about halfway through and somehow knew details that I hadn't mentioned. He does remember an older girl who came and played video games with him when he was a child.
But that's not the strangest part... He's 7 years older than me, which means I dreamed about this before I was even born. He said the only older girls who lived nearby who he played with are not deceased, which we double checked to be sure.
So, I'm not sure if I hijacked someone's body or memories or what, but I can't explain it and he can't either. He remembers this so called dream of mine, but he actually lived it and has never really given it much thought seeing as for him that would've been nearly 25 years ago.