People that consume a lot of THC daily, the dreams are not remembered in a clear way and the number of nightmares seems less impressive.
Many people say they don't remember dreams or nightmares.
I think the dreams and nightmares are not so conscious but they still happen.
I 'll use a very strange and simplified analogy like we eat and defecate as well as we receive a lot of impressions during the awake state and there should be some kind of discharge or maybe an unconscious form of catharsis.