I don't get motion sickness, so I kind of feel for the folks who get it even though I don't understand it personally since I've never experienced it(I just don't get motion sickness at all).
Now, that said, in Star Citizen, it's probably worse for people who do get motion sickness in video games because the camera sits IN the eyes of the avatar in SC, it's not the standard above the head placement that FPS games usually have. Combine that with the animation of the avatar being extremely realistic, and you get a lot of bobbing and swaying, which as it happens, it exactly how it should look, it's what we actually see in real life as you move around. Thing is, our brains filter that motion out and make it appear steady, and CIG is working on making that happen ingame, automatically filtering the motion, they just haven't gotten there yet.
I barely notice the movement myself, only when I stop and the view bobbles around a bit as my body comes to a full stop, just like a real human does...CIG has gone all out on the animations and making the view proper, still got some kinks to work out though. Ships, well, some ships have a slightly less smooth flight at certain speeds/accel values, so the view can be bobbing around a bit, especially if your ship has taken damage to the thrusters or main engines or the piping between them as all thrust is actually produced by the main engine and piped to the thrusters, so a hole blown in your hull through one of those pipes can cause thrust at the broken section instead of the thruster when you try to use it. Anyone who get motion sickness would have been sick as hell yesterday watching me fly after I got half my ship blown off. 1 of my 2 main engines was gone, all the thruster points on that same side of my ship(right) were gone, and there were holes in my hull all over the place. I could get forward thrust going and keep the ship going generally where I wanted, but the moment I tried to slow down, my ship would go nuts and just start spinning out of control as the busted piping was causing all sorts of uncontrolled thrust to happen. I actually got from where I was shot up to a CryAstro station via QD(don't ask how I managed that, stuff literally broke while in QD from the stress!). I was around 5k from the repair pad when I realized I had way too much lateral thrust taking me to the right(relative) and tried to counter that....more stuff broke(heard 2 distinct explosions) and suddenly I was spinning wildly around the center axis left to right and going over 400 m/s(twice my normal top speed!). I finally got the ship back under control 25k away from the station and headed back. I was literally about to land and get repaired when some prat decided my ship moving at 1 m/s was the perfect target and starting firing on me. I hit the brakes....realized that was a mistake as my ship starting spinning around wildly again and simply waited it out. 3 minutes later the prat finally blew my ship up. Not as easy hitting a wildly spinning Cutlass that's already half blown up as you'd think it seems
So, for now, if you suffer motion sickness in video games sometimes, you MIGHT want to avoid SC until they get the avatar animations/camera down better. And, well, since they are doing a far more detailed ship flight/damage system than E: D has, you MIGHT want to avoid SC totally. This wasn't the first time I've had thruster issues due to damage to my ship, and it's just going to get MORE realistic as time goes on, so it's not really a good idea for people who get motion sickness to play, unless you stick to manning a station inside a ship that doesn't show you the movement, of which there are quite a few. MOST of the multicrew ships have crew stations without outside views, so you'd be good on those.