Why do we get car sickness?
Your eyes tell you youre moving, but your sense of balance tells you you’re standing still. This conflict makes you ill.
Good answers here, but I’ll add one important thing:
The reason we get _sick_ is that many poisons cause our inner ear feedback to not match what our other senses are telling us. When that happens, your body goes into “poison control mode” just in case – specifically, wanting to vomit up whatever you ate that is poisoning you.
In simple terms, it’s all to do with the lack of control. You can make all the same movements when you’re driving the car yourself and not feel sick at all because you’re *expecting them*. Your brain knows what you’re doing and what’s happening.
When someone else is in control, you can’t anticipate their movements and, if there’s a lot of changes of speed, it messes with your balance and confuses your brain. It doesn’t know how to react as the movement is unnatural.
Cars and moving at those speeds (with such frequent movements and changes in speed) isn’t a natural thing, so our brains don’t always react to them properly. Unfortunately, as already mentioned by someone else, the brain thinks up the only ‘reasonable’ possibility it can come up with which is “*Gasp* Poison! Evacuate everything in the stomach, we’re in danger!”.
When the signals from your inner sense of balance conflicts with the information from your eyes, it causes a conflict in your brain which causes the nausea.
For example, when you’re in a driving car, your sense of balance tells you the car is making all sorts of turns, motions, and accelerating / stopping forces that you sense. But if you are staring at your phone with your head down and all you see is the cars interior your eyes don’t notice any movement. So you get carsick.
If you were to stare out the window you’d be much less likely to get sick because the signals from your eyes and sense of balance would match.
It has to do with our inner ear fluids, which tell our brains our orientation in space (up/down/around/etc). In a conveyance, such as a car, sometimes those senses get all confused because the body is stationary (0 mph), but the eyes and inner ear fluids are sensing that we’re moving a lot faster than 0 mph, so stuff gets weird.
Our bodies/brains developed before such fast conveyances were a thing, so they have to cope.