In what ways can a person express symbols and metaphors unconsciously?

There are several ways to approach this question. By "unconscious" expression, we may be referring either to unconscious patterns of speech and use of autogenic (self-generated) metaphor without deep consideration, or we could be referring to truly unconscious generation of symbolism, as in while dreaming.
Studies have found, particularly in connection to the developing psychological discipline of symbolic or metaphor therapy, that humans do tend to use analogy or metaphor to describe their own experiences. Rather than using an existing metaphor, it is very common for an entirely new metaphor to be generated from whole cloth which the person unconsciously thinks is a better fit for their situation than any existing metaphor. We can also see this happening in the tendency of people to use "mixed metaphors"—whatever they have said, while not internally logical, is a better representation of their mental understanding of the situation. For example, in describing a sense of being unable to control one's life, a person might say, "I feel as if I am trying to drive a car which has no steering wheel." This provides an interesting insight into how exactly the person feels out of control. A psychologist might query it further: "There's no steering wheel. Is there a brake?" A feeling of being in a car with a steering wheel but no brake represents something different to being in a car with a brake but no steering wheel, while being in a car with neither would be the most extreme form of lack of control. Our personal metaphors, and the theory that we will unconsciously choose the most specific and accurate possible metaphor for our own situations, can offer a unique insight into our mental landscapes.
There is also the question of where these metaphors were first presented to us. Sometimes, our waking unconscious does suggest such metaphors, but Jungian theorists suggest that it is often while dreaming that symbols and metaphor are first processed and presented by our unconscious minds to our conscious ones. A dream can be an unconscious expression of symbolism and metaphor which helps us appreciate what we are concerned about, or how we perceive the universe around us. Our dreams will often take symbols from the world around us, whose meanings are widely understood, rather than personal symbols. This would include the symbolism of being in the dark to represent fear or uncertainty, or the association of a particular person with a type of animal, and so on.
Humans can also express these symbols and metaphors unconsciously through artistic output. While many creators do, of course, use symbols and metaphor carefully and deliberately, Freudian criticism takes the view that an analysis of a writer's output can be illuminating for the reader, as it enables us to perceive not only what the writer meant to be put there, but what was put there unconsciously. Through breaking down the symbolism and metaphor used by a writer and connecting these to his or her biographical history, Freudian criticism seeks to add insight into a text by determining the unconscious connections between it and the mental landscape of the author.
http://www.theemotionmachine.com/our-world-of-symbols-and-the-unconscious-power-of-dreams-art-and-mythology/