There are many people who, at the prospect of getting into a car (especially if they have to carry out a route full of curves), must take a biodramina to avoid dizziness and, eventually, vomiting.
But why do we get dizzy when we go by car or in a vehicle that is in motion, such as a boat? And, most importantly: why can dizziness translate into vomiting? What does our body gain by vomiting in such a situation?
Proprioception
When we travel by car, for example, our brain does not capture the typical movement associated with walking , that rhythmic swaying, because we do not really generate the movement with our legs.
Thus, proprioception (the sense that informs the body of the position of the muscles, is the ability to feel the relative position of contiguous body parts), is not originating the signals that serve the brain to understand what is happening. That lack of signals is reinforced by the fact that our eyes tell us that we are not moving.
However, the movement is occurring because a fluid in our inner ear is responding to the forces caused by the movement and acceleration of the vehicle.
Vomiting
But what do these mixed signals have to do with vomiting? Those signals are managed by our reptilian brain, the most instinctive part of our brain. So it acts in a very elementary way against the contradiction of signals.
If we are still and yet appear to be moving, the reptilian brain simply interprets that some substance is not leading us to believe that. Probably some poison from nature that profoundly affects our inner workings. As Dean Burnett explains in his book The Idiot Brain :
Poison is bad and, if the brain believes that our body is poisoned, it finds only one reasonable response to such a situation: get rid of the toxin, activate the vomiting reflex, and as soon as possible. The more advanced regions of the brain may know better the real situation, but considerable effort is needed to modify the actions of the more elementary regions when they have already been started. They are "fixed customs", almost by definition.