The mind creates a representation of the physical world, and that representation can be regarded as a layer of abstraction on which thoughts operate. Interfaces of that representational layer are consciousness and imagination. Imagination is the interface from thoughts, and consciousness is the interface to the outside world. The waking mind interacts with the outside world, and that interaction makes it conscious. The sleeping mind is unconscious, because it doesn't interact with the outside world. The sleeping mind develops itself, and that development is experienced as dreaming.