Space sickness was a condition caused by being off of a planet's surface. Its symptoms included nausea, dizziness, and disorientation.
Space sickness was often brought on by turbulence on a ship, or inertial dampeners being out of alignment, and was especially strong if a ship lacked artificial gravity. In many ways, space sickness was the deep space equivalent to sea sickness. Just as an experienced sailor was said to have "sea legs", experienced space travelers were said to have "space legs". (ENT: "Sleeping Dogs", "The Xindi", TOS: "The Lights of Zetar") Nonetheless, most space travelers experienced space sickness from time to time. Space sickness could be treated by inaprovaline. (VOY: "Relativity")