You just don't remember them...Those are called level one dreams that take place in the ego...AKA the dumbest part of your brain. level one dreams are almost never remembered and they are always about things you've seen earlier that day and really have no meaning like the level 2-4 dreams. The body always dreams, it's your brain way of communicating with your brain...yeah it is. As far as weed is concerned, I don't know enough about weed and it's relationship to dreaming, however I do know that as an avid and constant herbalist I rarely remember my dreams. Here's a neato snippit of dream knowledge...
Level One dreams-Ego's way of communicating to your body in now meaningful sense, basically a recurrence of images and sounds recently received by the brain.
Level Two-Dreams in the id...The most common dreams which are messages your brain relays to itself. The meanings are usually extremely easy to detect, such as if you were going into debt in your life your dream may be you struggling with something like trying to stay afloat or drown.
level Three dreams-These take place in the super-ego and they are very complex and the meanings are extremely subtle, these dreams are usually always remembered and they are usually remembered as extremely odd. These are the dreams that you may find yourself flying in or see objects talk or anything else that is not of reality.
level four dreams- This level of dreaming has not been proven scientifically yet. It is theoried that level four dreams take place in every part of the brain and that they all work together to display a premoniton. This is said to be where all pyschic dreams come from and also the origin of nightmares. This realm of dreaming is usually only witnessed in people who are having very depressed or otherwise negative times in life and this is the brain's way of survivng and either by telling the person to forget about those feelings or scaring them out of it. It's the brain's last resort to keep itself sane. Pretty cool, huh?
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"To solve world peace, all we need is like a couple trillion beans."
"The Mind is like a parachute, it only works when it's open."
PLUR - The Meaning of Life.