What causes motion sickness?
You get motion sickness when one part of your balance-sensing system (your inner ear , eyes, and sensory nerves) senses that your body is moving, but the other parts don't. For example, if you are in the cabin of a moving ship, your inner ear may sense the motion of waves, but your eyes don't see any movement. This conflict between the senses causes motion sickness.
You may feel sick from the motion of cars, airplanes, trains, amusement park rides, or boats or ships. You could also get sick from video games, flight simulators, or looking through a microscope. In these cases, your eyes see motion, but your body doesn't sense it.
Source: http://www.webmd.com