As someone who is strongly affected by motion sickness all my life, I would unfortunately consider myself as a kind of expert on the topic. I would like to list a few of my observations on the topic. I hope it is informative or even helpful. As a physicist, I am not a medical expert, but at least a careful observer.

- I am extremely sensitive. Sometimes driving as little 3 miles as a passenger in a car make me sick.

- I have no doubts that motion sickness is caused by the sensoric mismatch between the eyes and the sense of equilibrium. Other sources of sensorical input play a role though (you can sense a vehicles motion with your butt for example).

- as the driver I get much less motion sick than as a passenger. Under normal circumstances I don't get motion sick while driving, but unfortunately it happens from time to time. Bad traffic, darkness, empty stomach seems to be causes there.
As the driver, I not only have the additional feedback through the steering wheel, but also I am the main guide of the motion of the car. Accelleration and decellaration are directly caused by me, same with turning into curves.

- the nauseating effect is strongly coupled to the frequency of the motion. There was a link on HN some years ago to a paper which claims the maximum is at 5hz (I might misremember the number). This matches my experience well. I notice a strong dependency on the speed of the car. About 80kph (50mph) seems to be the worst. Going faster usually is easier on my stomach. Equally, I like stiff suspensions, soft ones are killing me. (Strangely, I never got sick in an Audi yet).

- same applies to some extend to boats. Yes, in my youth I acquired a sailors license, consider me crazy. Cruising against the wind is much less a problem than on rear wind courses.

- of course, I can't read in a vehicle.

- when I get truely sick, my stomach is off for hours, if not even till the next day. I think the theory that the body reacts to an imagined poison sounds very plausible.

- I do get motion sick in basically any vehicle. In trains much less than in busses, but even in trains I can feel uncomfortable. In both cases, it helps a lot to stand and not sit in the vehicle. You get the additional sensorical input from your feet (the sensor input of the feet plays the major role in the ability to stand upright and walk) and of course your hands holding to a grip. The effort for the brain to keep standing seems to be very helpful in convincing it of the real motion going on.

- I can watch 3D movies in cinemas. Only rarely I get a minor nausea which passes quickly. I have severe difficulties playing first person 3D games on the computer. Seems my brain can distinguish those cases.

- another strong point towards the irritation theory: I am rather sensitive to scrolling on a computer. With the first optical mice, I got quite regularly sick, as their motion on the screen not always followed the motion of the mouse. Those problems have vanished with later generations of optical mice. Erratic scrolling or screen reactions can still make me quite sick.

- in general, having lots of fresh air helps somewhat in not getting sick.

- there are of course psycological factors. But it has certainly nothing to do with "fear". I actually get less sick when a car drives fast (>70mph) as long as the driving isn't too erratic. Its the frequency of the motion. You do of course get quickly sick, if you start listening for symptomes. So please, don't ask someone who is sensible to motion sickness whether they still feel well... A mild distraction can help, a strong distraction, distracting from noticing the motion can be counterproductive. I usually like listening to conversations, participating can be a risk.

- motion sickness causes apathy. So if you know someone being sick, watch them. They might run into a car, fall from the boat and not care.

- sometimes it does help to lie down and close the eye. This can reduce the irritation as it takes the eye input out of the game, and your back provides additional sensoric input.

On the prevention side, if I want to travel except when I am doing the driving, e.g. air travel, I had the best results with Cinnerazine. Taking a single capsule of 75mg per day, at least 3 days in advance of the travel and continuing during the whole travel time has great results. This allows me, with some care, to use modern means of transport like a normal person. I am not totally immune, a colleague driving me up to Alices and La Honda from San Jose made me feel pretty bad, but I recovered reasonably well, though I felt uncomfortable for the rest of the trip. On the other side, I noticed me once texting on the back seat of a cab racing through Taipei, without any discomfort. YMMV.

I would be happy to answer any questions. As said in the beginning, I am not a medical professional, in doubt please ask a doctor, I just have tons of experience on that matter.