Have you been thinking about 2012 and the "end of the world" hypothesis lately? That's probably a logical explanation to why you dreamt this.
This was probably your imagination creating a possible scenario should the event occur. As for the darkness, maybe there was a real-life connection with being in the dark, perhaps being a bit frightened? Sometimes, the littlest occurences can become vivid and revisited once more in a dream. This is odd sounding, I know, but it's not impossible..

Frankly, the best thing to do though, if you are concerned about your dream, is to brush it off your shoulder and move on asap.

Be well!