While they body is quite good ad coping with positive g's, there are certain subsystems that are particularly vulrenable to negative g's.
Severe redouts will rupture the delicate blood vessels in the eyes - and according to my father, who's an eye doc, the red out (which we all know is caused by the blood) doesn't go away in a second.
What I mean with hanging in the air is the enemy goes the wrong way - i.e if he rolls his plane, you expect the next move to be a positive g pull, meaning he'll move in the direction his canopy is directed - but instead he pulls many negative g's, and goes in the other direction (sort of).
Guess my view on this is pretty clear, but that doesn't mean it's the only one, or correct one.