Steve
Its something you have to build up to! I can remember after ages of flying straight and level accepting an aerobatic flight in a firefly.
My friend a very accomplished aerobatic pilot did the lot with him flying and me as a passenger. We got to snap rolls and that was it I felt as sick as a dog.
" Your turn he said gleefully"! I had to bow out until we had flown level for about twenty minutes when I felt fine. With me in control it was a different matter NO sickness.
We all have different tolerances and can strengthen those tolerances by flying aerobatics.
I can remember flying some PAX in a Seneca twin to Newcastle. Warned of one PAXs inability to take any motion I was relieved as the air was calm and smooth.
No way the guy projectile vomited all the way there covering every inch of the rear compartment.
An airline cleaning company took pity on us and cleaned the aircraft for us up at Newcastle.
The return journey the same but thankfully the guy had not got anything left to spew up.
Your comment about being sick in a bag and getting on with it is very relevant to overcoming the problem as fear is the basis of most things.
Pace