I'm a generally habitual pot smoker who has long periods of sobriety due to switching jobs or a few times to support my wife during her pregnancies and I can say that without fail about a week after I stop cannabis I start having super intense dreams for about two weeks then normal dreams after that. When I go back to smoking, I stop dreaming after around a week of use. My sleep quality generally increases without cannabis but I do have ptsd associated nightmares, sweating, yelling etc. Cannabis completely stops my dreaming but I need like 9 or 10 hours of sleep to feel as rested as I do with 6 hrs sober.