Non existent people apparently you know?

I've encountered different people in my dreams that apparently, I knew. Like if that person was part of my life, I knew their background stories, personality, my relationship with them, everything.

For example, I had a dream in where I was running from an old man with a white haired young girl, our relationship was short, I only knew her for a few days but I knew what we were doing (sadly, those memories vanished upon waking) I remember that my father was with that man and told me to give them the girl, that she was a witch or something, so I felt this urgue to protect her because of our friendship, I really felt sorry for her, I was sad that she was being persecuted. Then I woke and realised this person isn't real, the feelings I felt in the dream were gone, and so were the memories, I don't even remember her name.

Does anyone else experience these things? it's pretty interesting to remember these kind of dream characters while awake.

I've had that in non-lucid dreams. In lucids my normal waking memory is there so I think it's different. I say I think it's different because I haven't had the effect you are talking about in a non-lucid and then become lucid in that same dream. I suspect the effect would be a bit like waking, I.e. I would forget who the person was perhaps? You didn't say, but I assumed you were also talking about non-lucids?
How much of what you think you know about these characters is real? That is, for me, I can fool myself, in the stupour of a non-lucid, that I know lots about the person, but actually perhaps I don't, it's just a strong (false) sense of knowing them?

Yep, I was talking mostly about non lucid dreams. Now I think of it, what you said makes sense, I always assumed that I knew a lot of them but I simply forgot, when probably it's just a sense of knowing them. You've just enlightened me.

I've found this happening me a few times. I'd be talking to someone and I would remember my whole past with them, even though I've never met them before. I'm one dream, I remember working with someone for a job and when I try to, I can recall our training together even though I've never met them before. I caught this right before I got lucid.

My theory is that it's something similar to what happens with split brain patients in this video: https://m.youtube.com/watch?v=wfYbgdo8e-8 where your brain makes something up to explain away an inconsistency.

Not really. However whenver I revisit certain planets my DCs will remember me or if a long time has gone by, their descendants will remember me and talk to me casually. Its only ever happened during a non lucid, but never in a lucid.