Doesn't happen to me, but I've ended up in a black void where I'm spinning and floating.
On another forum they said this might be the "3d void" and that it was a stepping stone
to one of the higher realms, which sounded exciting to me, but I never got back there.
It does sound to me like you also could be getting an invitation to expand and explore
in the astral, rather than the typical dreamscape. Of course, this is all speculative.