The Devil definitely can speak to our minds while we are awake. He'll deafen and protect our sleeping minds from all others. And, of course, God as Creator, can simply nudge the workings of our mind to result in the message He wants us to receive. This probably opens a lot of theological, physiological, and psychological questions that we need to avoid for the purpose of this answer. The very nature of dreams might help us understand their significance.
Dreams are sensory.
We only dream what we have sensed and are able to sense. A person who has been blind all his life, never has dreams in which he sees something. It is impossible. Helen Keller s dreams consisted only from what she could sense through touch. This shows the naturalness of our dreams, but also shows how our dreams are influenced by our senses.