It does make you tired, and a full day of heavy smoking will definitely leave one very tired and likely easy to fall asleep, but as said, it isn't the best kind of sleep really (I wondered why I would feel groggy sometimes in the morning, but I see the technical explanation now!) I don't dream very often at all, it's rare, since I started smoking daily the past couple years. The odd day where I happen to not smoke any I can be sure I'll have some dreams.
It doesn't really make you tired or knock you out when you smoke it all the time. And when you're withdrawing from killers, you can smoke all you want and still won't fall asleep at night.