I think about this a lot. Everything exists as a memory. The only reason Reality seems so real all the time is it is a constant feed, so to speak. Inside the dream it is so real! But when you wake up it is only a memory. Some memories are more vivid than others. But the difference between Lucid Dreams, and Reality, is one needs you to sustain it, and the other doesn't.
EDIT: And yes I have had fake memories in dreams a lot. Even in low-level lucid dreams. Moslty in normal dreams though. I had one last night, where I suspected I was dreaming, but then I got a fake memory that confirmed that it was real. Oops, it wasn't!