"Why do my dreams go away if I smoke cannabis daily for about a week? And then, why do they return so vividly if I take a tolerance break? "
According to an 2014 article on LeafScience.com, here is their answer to your question:
Marijuana and REM Sleep
The brain is most active during REM sleep and most dreaming is thought to occur during this stage. Numerous studies have shown that using marijuana before bed reduces REM sleep. Researchers believe this is why marijuana users report fewer dreams.
During the night, the brain cycles through 4 different stages of sleep, spending the most time in deep sleep (or slow-wave sleep) and REM sleep. The amount of time spent in these two stages is closely related. In fact, studies show that marijuana lengthens the time the brain spends in deep sleep, which leads to less REM sleep.
Ingesting THC or marijuana before bed also appears to reduce the density of rapid eye movements during REM sleep. Interestingly, less REM density has been linked to more restful sleep.
Most studies on marijuana and REM sleep have looked at the effects of THC. However, other compounds in marijuana may interfere with THC’s effect on sleep. For example, CBD has been found to promote wakefulness compared to taking THC alone.
What Happens When Quitting
Regular users of cannabis experience an abnormal increase in REM sleep when use is stopped. This is called the REM rebound effect, which leads to longer and denser periods of REM sleep. The REM rebound explains why cannabis users often experience highly vivid dreaming when trying to quit.
The sleep disturbances that occur during cannabis withdrawal usually begin 24-72 hours after quitting and can persist for up to 6-7 weeks.
Interestingly, the REM rebound is not unique to cannabis use. Other substances that interfere with sleep, such as alcohol and sleep medications, can cause REM rebound too. What’s more, people who are sleep deprived often undergo a rebound in non-REM sleep.
The rebound effect appears to be the body’s way of coping with being deprived of certain stages of sleep.