What are dreams?

The human body and all its functions are controlled by DNA. The genes and the proteins that are made from them cause all types of actions and reactions in our body. We sleep because our body's clock thinks that it's time for us to get some rest. However, considering the fact that the human body is 'modularized' already, why can't sleep be induced independently for every module. We have so many organs and systems in our body each of which serves a different purpose. But, when we sleep, everybody takes rest. Instead, we could let different organs rest at different times. Wait, how will this help?
Assume that we classify all our daily activities into two major categories: Hard-thinking tasks (CPU intensive) and Mundane tasks (I/O intensive). For example eating, drinking, bathing, etc do not require a lot of thinking, whereas thinking, studying, etc require brain but much less physical activity. Hence, when one type of activity is carried out, the other parts can rest. For example, the brain (except for a small part of it say) can rest while we are eating, bathing or doing any other mundane activity which doesn't require much thinking whereas we could be lying down resting our whole body except a major part of the brain when we are thinking. Is such a thing already happening?...
Dreams!! Are they the means of communication assumed by our sub-conscious? Is that how it conveys it's knowledge and information to the conscious? Was it my sub-conscious that intended to write this blog?!...