Motion sickness is one of the more familiar types of sensory integration disorder in humans; in motion sickness the brain is unable to reconcile the sensory information coming in from the eyes and the vestibular system; while our eyes see the world around us moving in one way, our inner ear is reporting that it is moving in a completely different way.
In car sickness, sea sickness, and air sickness, our visual system is reporting that our immediate surroundings are motionless, but our vestibular system is telling us that we are moving; in car sickness and sea sickness, the difference between what we see in out peripheral vision and in our central vision may also be a factor.
Motion sickness generally causes nausea, but may also involve cold sweat, headache, dizziness, and vomiting. It generally does not last much over an hour once the cause is removed, but some people continue to experience lingering symptoms for hours or days.
The simplest form of treatment is to focus on the horizon; this gives your visual system a chance to accurately judge your speed and movement. Closing your eyes may also help, although for some this makes matters worse. Other treatment suggestions tend to focus on preventing or managing nausea (eat dry crackers, avoid greasy food), or rely on medication, usually an over-the-counter antihistamine such as meclizine (Antivert) or dimenhydrinate (Dramamine), or scopolamine (as a patch).
There has been a recent attempt to rebrand motion sickness as neuro-ocular vestibular dysfunction or see-sick syndrome, in order to raise awareness that many people suffer motion sickness symptoms even when not in motion -- rapid action on a movie or TV screen, watching a 3D-movie, or walking through a crowd may trigger a response. However, the driving force behind this rebranding are the people who make money from lecturing on it and those selling special prescription lenses, and it has not been picked up in the scientific literature. The formal term for motion sickness is kinetosis.