Not the person to ask about sleep, but medications change my dreams big style. Mirtazapine makes it vivid while just 50mg Chorpormazine gives me nightmares every night, so maybe medication? if not, i'm not sure.
I've always been able to lucid dream, normal for me, I actually found I missed it at the start of DP, as I didn't have dreams. I know stoners and was one of my friends quit a while back and found it weird that he had dreams again as he hadn't for like 8 years! Brain chemistry is my guess.
I do enjoy a bit of dreaming. I don't see a problem with Lucid dreaming and having DP, as i said, I missed it when it wasn't there.
Nightmares if not medication is the cause, i'm not sure, but I know medications can stop it. Quietapine makes me not dream but I am sure that most people will find different things, cause more and less dreams. For instance Chroporamazine 50mg is the lowest dose, i'd say the average person doesn't wake up with a nightmare on it every night, or people wouldn't use it, just a thought and was enough for me to stop taking it very quickly.
Sorry this is medication angled. Might be no help to you at all