Less REM sleep
Marijuana users can get deeper sleep, but REM sleep is disrupted. It is characterized by the fact that we feel almost conscious and our eyeballs move quickly. The REM phase is also the time when we most likely have vivid dreams and nightmares. Scientists don't really know why this sleep cycle is beneficial to our health. But one of the main theories is that it allows the brain to rest, more specifically to the parts that secrete serotonin and histamine.