Vivid dreams that are so real about the unknown?

Hello, I just wanted to know what it is meant by when i have a dream, its about the unknown, they feel like so real, some of them I don't remember, there is one like of me going to mars and finding a relic and the others I just don't remember. There was also one of me fighting evil during the day of judgment and another one of me in an adventure about the unknown. What does it mean?