Ive been thinking about this. I have never had a full lucid dream, more like a little 5 second lucid experience 
. When you are in a lucid dream, and say you fly to space. Is it simply your imagination generating the images of space? Or if you meet a person that you dont know, like… jessica simpson 
. You probably dont know every detail of her body, so does your imagination simply make up the rest? Just curious…
Yeah. It tries to “make sense”, ie you don’t have to know and imagine each second every detail of Jessica Simpson 
to see her. I think it’s the subconscious or something to that effect…Neat function. It “fills” what you don’t know/can’t think about all at once.
I’d say that your memory makes “Jessica” or whoever as it remembers it, and then add some things that you believe is true during the LD.
I had an LD starring Alison Lohman 
yesterday and while i was in the dream i thought : " wow!! She is so like IRL…" but in fact she wasn’t. I only realized it when i was awake…
I guess your brain build false memories to full the holes… 