Consciousness is simultaneously the defining and most perplexing feature of the human mind. It raises questions about the true nature of humanity and life in general. If consciousness is just a by-product of the brain's neural network, then what separates humans from machines? If consciousness is just an illusion created by the mind, rather than a sign of a "soul," then does free will truly exist? The true nature of consciousness is seemingly impossible to define. Rather, studies concerning this topic tend to focus on what affects the degree of consciousness or different states of consciousness.
Just so we have some semblance of a working definition, we will posit that consciousness is our moment-by-moment awareness of ourselves, our thoughts, and our environment. It allows us to exert executive control over our thoughts and actions. We go through different states of consciousness on a daily basis--from sleeping to being wide awake. Different states of consciousness can also be reached through hypnosis (which can close the mind off to signals of pain, making the person in the state of hypnosis numb), meditation (heightened consciousness), and seizures (loss of consciousness). Selective attention, in which a person focused on one thing and loses perception of other sights and sounds in the environment, is also a form of shifting consciousness.
Christopher Nolan's Inception (2010) revolves around a very specific state of consciousness: the dream state. While the film takes many liberties with the "rules" of the dream world, it explores consciousness in a creative and symbolic fashion, and draws attention to the fact that even when we are not consciously aware of our surrounding, our mind is still able to create worlds of its own that seem adequately convincing during the dream.