Actually the whole WBTB thing is based on the idea that you can go to sleep and go almost immediately into REM sleep by already having your delta-wave sleep. It takes almost no time to have a dream- how many of us have heard our alarm, snapped it off, fallen back asleep and had what seems like an hours-long dream only to jump up 15 minutes after the alarm went off.

So with that in mind- sounds like an LD. Next time try to remember to look around you, and force your brain to keep rendering (so to speak) the dream. Even if you already looked at the room when you look around you again, touch objects and rub your hands, you're forcing your brain's attention on creating the world. This can help pull you back down when you start to drift away from the dream.