It could just be the way your body reacts. As if it goes in to some sort of shock as if your terrified of the drops. You may not even be subconsciously aware of it, but its like the mind and body have a way of protecting you of trauma or potential disaster.
It could be a sign of low blood pressue, as your going up, down left right and everywhere your body heart can't keep enough blood running to the head hence the blacking out. It could also be anxiety induced too.