I wonder if it isn't a physiological problem. I have always coped badly with negative g. One of the feelings was in fact a pit of the stomach sort of foreboding feeling. I get this when I have stomach problems too. All too often now I'm an overweight old fart. Some people just don't tolerate it so well. I was one of those though experience did help me cope with it. There are so many things in flying that are uncomfortable that we just have to grim out. I was bilious for my first few take offs. It wore off but now I don't fly very often at all it has come back. Concentration on the task in hand does help.