Last night I tried some sort of meditation thing before I went to sleep, and I had a sensation similar to yours, minus the voices, before I fell asleep. It was almost like I was sinking down into the pillow, farther and farther, as I became almost numb, (almost like a small amount of laughing gas), but still felt perfectly aware of my surroundings at the same time.

I would also like to add that that was the fastest I have ever been able to fall asleep. I can usually lay in bed and watch the hours tick by.