Dreams of Myth

So last night i had a dream and well, it was quite unusual. I felt like i was in Rapunzel. I was in a castle like she was but instead of one guy coming there were two. Except one was coming to save me and the other was coming to kill me. I really don't remember what all happened but all i know that the last thing that happened in my dream was one of the two guys had said "I love you" then put a gun to my head and that is when i woke up...It wasn't a dream, it was more of a nightmare.

Do dreams mean anything? Do they come true? How can you tell if a dream is supposed to mean anything when you dream it...what happens when you see things in reality that come true after you dream your dream? What does it all mean?