To dream about mucus generally symbolizes something that is burdening you that you may not be willing to vocalize or speak out about right now. This secret or thought is unhealthy for you to hold in, like as we know it is better to spit out mucus than to swallow it back down. Your subconscious is telling you to share your story, secret, or an opinion that you may have about something, since you are currently letting it affect you in a negative way.