Why do i throw up when i get motion sickness?

Vomit center: There are several neural connections present to help maintiain our balance. Unfortunately one of those balance connections goes through the "vomit center" in the brain stem. Motion sickness is due to sensory conflict (incongruous information from different sensory systems). When this sensory conflict occurs, it triggers an assortment of responses of which vomiting is one.

A=A: That's what motion sickness is. You get nauseous and often throw up.

Motion sickness: One theory is that it is a defense mechanism against neurotoxins. When we feel motion but can't see it, the inner ear transmits to the brain that it senses motion, but the eyes tell the brain that everything is still. As a result the brain concludes that one of them is hallucinating & that the hallucination is due to poison ingestion. The brain responds by inducing vomiting to clear the toxin.