If you lose the dream scene and end up in a black/white/grey nothingness then that’s commonly refered to as the void. I’ve read about some people having multi-coloured fractal style visions as well, which sounds cool. (Mine is just black or grey)
The key here is to relax, not panic about it. This is merely a new dream forming. If you can remain calm and patient, the dream will continue and your body will reform. Even better, attempt to visualise a scene or a place you wish to go.
Jer - if you lose your body but are still in a dream scene then you could attempt to possess another DC or simply ask (or demand) out loud to your subconcious to give you a body.
Here an article about dream control that might give you some ideas on how to overcome this.
EDIT: You could also google ‘lucid dreaming the void’, which is what I did when this first happened to me.