Well, while we're on the topic:
Motion sickness usually comes from one of 2 things -- a hyper-sensitive inner ear, or the way your brain processes motion in your peripheral vision.
I'm very slightly in the latter category, as are most people who get sick from a visual cue. I can ride roller-coasters. I've been on boats (big and small) numerous times. I used to do martial arts requiring rolls, spins, and leaps. I've been skydiving 6 times. I've ridden in an decommissioned F-15 and been through snap rolls and split-S turns...
Nothing. Not a thing. I can simply enjoy the ride. Games don't bother me at all. What gets me is trying to read or write in a car. Not trains or jets or buses or boats...just small land vehicles. Can't do it. I vomited on multiple occasions when I was younger.
The secret, which I discovered when I was almost 30, was blocking my peripheral vision. On a bus, boat, or jet, you don't see the motion out the window on both sides of your head, so you're brain doesn't really process the fact that you're moving through your eyes. In a car or truck, your peripheral vision is detecting motion on all sides. When your eye tries to find a focal point, your brain detects motion on the periphery but an unmoving point at your focus and gets dizzy/nauseous/etc. It can't tell if you're standing still or not. If you block your peripheral vision, it helps the brain to focus on only "point" at a time and gets rid of the pseudo-motion it thinks is happening. If I put sunglasses on -- I can read or write in a car without issue. It creates a near-focus field that my eye detects and treats everything I see in my periphery like a movie screen.
TL;DR
Block out your peripheral vision by playing in the dark or try putting on a pair of sunglasses while you play (just don't use polarized lenses). Either way, try to make the screen the only focal point and remove anything (especially things that might be moving on their own -- like a clock pendulum or whatever) from your peripheral vision. See if that makes it better.