Knievel77, I'm rarely on here these days, but I think you may have emailed me personally. ;-) Anyway, I'm a helicopter instructor; I also have a degree in psychology and know a teeny bit about phobias. Oh, and I'm scared of heights in some situations, though not in a helicopter unless flying low over hills followed by valleys or throwing the aircraft off a pinnacle.
Anyway, enough of my qualifications. I wanted to say that in my opinion your instructor who banked the aircraft sharply to show you that R22s could put up with it should be shot! At any rate, find another instructor. That's not how you deal with phobias. All that does is scare you, convince you it's scary, and confirm in your mind that you were right to be frightened. In other words, it makes matters worse.
The usual way is to take things slowly and gently. Get used to flying straight and level with a sympathetic instructor. When you feel OK with that, then bank the aircraft a few degrees. When that's alright, try more. If you start to sweat or feel bad, stop. In other words, push yourself to your comfortable limit, but not a millimetre further...or things can get worse.
This worked for me in getting used to climbing ladders and similar. I still don't like it much, but I can do it. About the grabbing for support in a turn, I've had trial lesson students do that, often. One grabbed me in a complete panic once, which wasn't nice! I then learned to take things very slowly until I knew he/she was OK with what was going on. So you're not unique. But it may take time. And at £300 an hour, it may cost. I don't know what you can do about that, other than accept it, if you want to fly helicopters.
Good luck!