bit of left field but I wonder if it is worth trying graduated exposure to the particular motions and build up tolerance?
eg sit on spinning chair while doing head movements or if you can, getting some time in an aircraft while doing the head movements. Stop when you feel queasy, wait till feeling OK and try again (hopefully for a bit longer each time until your tolerance builds up over a week or two).
Tolerance tends to decay too if you are not exposed to the motion that causes it for a while.