I find Coca Cola and salt and vinegar crisps help. I also used to have one of those wristbands with the button that pushed into my wrists. I've never been on a tilting train, but those things did help on ships. I used to get very sick on ships, now I don't. Interestingly I still get sick in cars and buses when I can't see out of the front or have a wide view.
It's an individual thing really. Avanti isn't running a cover-up operation, which would be on a similar scale to the alleged cover-ups regarding the moon landings and the shape of the Earth... Some people will feel sick, but there are ways to get around it. Personally I wish the trains had opening windows as fresh air also helps - then again, I generally prefer opening windows to air conditioning anyway as on fast trains I prefer the feeling of the wind, but that's just me.