I suspect that when the aircraft initially stalled, the 1g acceleration earthwards would have created a "falling sensation". However once the aircraft reached terminal velocity downwards there is no further acceleration just a downwards velocity vector. Then there is no acceleration hence no "falling" sensation anymore. How long it took to reach terminal velocity, no idea. Someone cleverer than me can probably calculate it with the right data. I'm guessing the Captain rushed back up front when he felt the vertical acceleration before terminal velocity....