What does this dream mean?

Me, my brother and my cousin were walking in the woods, my cousin went into an ancient aztec like cave, and got shut in there, forever, to die. Later on it was raining non-stop, and the world was falling apart. My family was dieing one by one, my brother was walking down the street towards me crying and got hit by a truck. There was a safe place where I could possibly be safe, it was in New York, I packed my bag and was going to start walking there. [I live in VA] It was in the middle of the night and I went to tell my mom good bye and that I loved her, and she said "[my name] I love you so much." and I just could't leave, so I went and laid in my bed waiting for the world to end. And I woke up. This was a terrifying night mare. I've been having a lot of night mares laterly, but this one I can vividly remember. And my best friend is having night mares about his girlfriend cheating on him and leaving him, and my boyfriend is having night mares about the same thing. Is there any way they are all related? And what actually is a dream? Do they mean anything? I heard they signal events that are to occur in the future, maybe not directly but they hint at things. Is this true? And what does my dream mean? And by the way it was raining last night when it happened, and it was rainging in my nightmare.