Why do some people get motion sickness in cars, boats, or planes?

The vestibular system in the inner ear detects motion and balance, while vision and body pressure also tell the brain what is happening. In a moving vehicle, these signals can disagree, such as when your inner ear senses movement but your eyes see a stable interior. The brain interprets that mismatch as abnormal, and the result can be nausea, vomiting, and cold sweats. Motion sickness is especially common in boats because of continuous rocking, but it can happen in cars, airplanes, or virtual reality. Looking at the horizon and facing forward often helps reduce symptoms.