Human beings are 'self-organizing' systems forced to interact with an environment that is always changing. We seem to use the dream state as 'training wheels' in exploring and making any changes. Life's natural movement toward entropy is unfolding all around us, even while we try to achieve stasis and a sense of the familiar. In higher organisms (like humans) this pursuit of stasis is achieved through the nervous system. Dreaming offers a sensory vehicle to process anxiety in a safe environment. Anxiety is a common theme in dream specifically because it is one of the most important reasons for dreaming. When disturbing things happen in our dreams, they are meant to do just that: disturb consciousness and help us to let go. See Nightmare, Answer, and Attack or Being Chased.