This is for smaller aircraft pilots, but the principles still apply:
https://www.aopa.org/go-fly/medical-...otion-sickness
Motion sickness is the body's natural response to a disconnect between the middle ear's balance mechanism and other body senses of motion (muscle "position sensor" nerves, vision). In our evolution before "vehicles", the most likely cause for such a disconnect was ingesting poisonous food, so the evolved response is to empty the stomach ASAP. Perceived warmth (fever), a subnormal amount of oxygen (think: cyanide) and smells (rotted food) also make the body believe it is poisoned, so removing as many of those cues as possible is good.