Actually it's now known that dreaming occurs during every stage of sleep - it's just that different sleep stages produce markedly different types of dreams. REM sleep is the most familiar - the dreams that are like movies, and mostly that's when lucidity occurs. But during N-REM (non-REM) sleep we still dream, though it has a distinctly different quality to it. Usually there are no visuals or we simply observe static geometric shapes or mandalas. And rather than stories, this type of dream is composed of thoughts... basically just a string of thorts () running through your mind. These dreams seem to be much harder to recall than REM dreams.