I have had something like that happen but it in no way felt as if I was lucid. "Dementia" isn't the right word, but it's the first that comes to mind. For those of you who haven't had something like this happen, it feels (to me) much like a dream where I am being chased. Instead of running away from pursuers, however, your mind is racing to find out what the hell is going on... When I wake up from mine, I get that kind of "Holy sweet grace on high! I am SO glad that was a dream" feeling...

Dunno if this is what you are talking about but that's my experience...