I call it "Seahorse Sickness"!!!
It is...getting seasick...only I am on a horse!!! Yes, I get carsick too, but water motion (boats) is the worst! Small planes and helicopters 2nd and riding horses 3rd. I can not lounge a horse on a lead line nor can I ride in the arena too long round and round and ROUND!!!
There are many options out there in the market place to combat this ailment of mine including but not limited to the following!

Seabands!!! The way this works is by acupressure...the white dot presses on a spot on your wrist that is suppose to suppress the motion sickness!
I never ride a horse without taking a BONINE and if the trail has lots of switchbacks or drop offs...I will wear the bands!!!
However...this Cowgirl will ride until she BARFS...and has!!!
Your Desert Rose!