Editing Motion sickness (section)

====Space motion sickness====
{{Main|Space adaptation syndrome}}
Zero gravity interferes with the vestibular system's gravity-dependent operations, so that the two systems, vestibular and visual, no longer provide a unified and coherent sensory representation. This causes unpleasant disorientation sensations often quite distinct from terrestrial motion sickness, but with similar symptoms. The symptoms may be more intense because a condition caused by prolonged weightlessness is usually quite unfamiliar.{{citation needed|date=July 2021}}

Space motion sickness was effectively unknown during the earliest spaceflights because the very cramped conditions of the spacecraft allowed for only minimal bodily motion, especially head motion. Space motion sickness seems to be aggravated by being able to freely move around, and so is more common in larger spacecraft.<ref name="Benson 2002" /> Around 60% of [[Space Shuttle]] astronauts experienced it on their first flight; the first case of space motion sickness is now thought to be the Soviet [[cosmonaut]] [[Gherman Titov]], in August 1961 onboard ''[[Vostok 2]]'', who reported dizziness, nausea, and vomiting. The first severe cases were in early Apollo flights; [[Frank Borman]] on ''[[Apollo 8]]'' and [[Rusty Schweickart]] on ''[[Apollo 9]]''. Both experienced identifiable and quite unpleasant symptoms—in the latter case causing the mission plan to be modified.{{citation needed|date=July 2021}}