The horseshoe is a lucky symbol and, traditionally, if it is turned upwards it represents the moon and protection from evil.
When turned downwards in a dream it is thought that power will drain out of the horseshoe, bringing you bad luck.
However, the above can only really be true in your dreams if you already know these superstitions. For most people the horseshoe is a vague symbol of good luck, often connected with weddings, so it could be that you are feeling subconsciously lucky or that you’re thinking of marriage or someone’s wedding.