I keep dreaming the same dream over and over?

I've had the same dream about the world ending a couple of times now. There was a huge earthquake and then a tsunami. People started panicking and then aliens came down in spaceships and saved us. I wake up every time right when we're about to land on their planet. It looks like Earth except there is no people on it. Oh, my dream always begins with me waking up and looking at the calendar. The date is December 21, 2012. What does this mean? I think it's weird that I keep dreaming about it..