This has been happening pretty frequently for me in my LDs. In the few that I have, everything's going great. I'm making sparks come out of my fingers or flying or getting ready to have sex...then the lights go out and I'm in pitch black for a few seconds, then wake up out of the dream. When I wake up I'm like fully rested, so my LDs seem to occur right before I'm supposed to awaken.

In the dreams it's happened for a number of reasons. 1) It just starts to fade out into darkness for no apparent reason. 2) I flew into the night sky and it was really dark. 3) Someone actually turned off the lights in the room and it got dark.

I don't know how to stop it because usually when it gets dark, I'm only like a second away from waking up so there's no time to react. Is this happening because I'm actually just waking up or could my dreams actually last longer?