Why do we get motion sickness?

The answer

Motion sickness is caused by a sensory mismatch between the vestibular system (inner ear detecting motion), visual system (eyes detecting motion), and proprioceptive system (body position sensors). When you read in a car, your vestibular system detects acceleration and turns, but your eyes see a stationary book; the brain interprets this conflict as a potential hallucination caused by neurotoxin ingestion and triggers nausea as a protective vomiting response. This 'poison theory' explains why the emetic (vomiting) response, which would be useful for expelling a toxin, is activated. The driver rarely gets carsick because their visual input (watching the road) matches their vestibular input. Approximately one-third of people are highly susceptible to motion sickness, while about one-third are resistant. Interestingly, people with complete bilateral vestibular loss (no inner ear function) are immune to motion sickness.