What does this weird dream mean?

I keep having end of the world-type dreams. The other night I had one about an alien invasion and trying to save myself and the people around me. It was so realistic it was scary. I also had a dream before that my town had a massive flood and there was a secret government that you had to beg to keep alive. I just keep having Random dreams about the world coming to an end. I wonder is this a preminition or what? Btw, I have had dreams come true before. Usually months after I've had them. I dunno, any thoughts?