A couple of things come to mind, one is that I have been told when you dream about things like being thirsty or needing a restroom it is a physical need at that time. Mouths get dry when we sleep.... My opinion on the other is that it is something you feel guilty about and embarrassed and it presents in your dreams (bedwetting). Even though it is a medical condition you can do nothing about it bothers you. I imagine the smoking is related to a craving just like food, alcohol, or tobacco, your body wants it and is trying to let you know.... I am not a doctor so these are just educated guesses, I have done dream analysis research also in the past. Hope this helps.