I'm not sure if everyone was talking about the same kind of void, but the kind I have experienced was like this:
When i was a baby I was adopted. I never knew my birth mother nor did I ever feel compelled to know her, until a time in my early 20's.
For about a 3 week period I existed with a void, not a phsycological one, I mean a strong sensation in the center of my torso.
Once I was aware of it I turned to my wife and told her "my mother is gone" without even thinking about it.
We started to search for her after that, but never dug very deep...I suppose that I jsut knew.
or maybe it was gas??