If so, consider yourself pretty lucky.

For about one-third of the population, looking at a book while moving along in a car, or a boat, or train, or plane, quickly makes them sick to their stomach.

But why do we get motion sickness in the first place?

Well, believe it or not, scientists aren't exactly sure.

The most common theory has to do with mismatched sensory signals.

When you travel in a car, your body is getting two very different messages.

Your eyes are seeing the inside of a vehicle, which doesn't seem to be moving.

Meanwhile, your ear is actually telling your brain you're accelerating.

Wait, your ear?

Yeah, your ear actually has another important function besides hearing.

In its innermost part lies a group of structures known as the vestibular system, which gives us our sense of balance and movement.

Inside there are three semicircular tubules that can sense rotation, one for each dimension of space.

And there are also two hair-lined sacks that are filled with fluid.

So when you move, the fluid shifts and tickles the hairs, telling your brain whether you are moving horizontally or vertically.

With all these combined, your body can sense which direction you're moving in, how much you've accelerated, even at what angle.

So, when you are in the car, your vestibular system correctly senses your movement, but your eyes don't see it, especially if they are glued to a book.

The opposite can happen, too.

Say you are sitting in a movie theater and the camera makes a broad, sweeping move.

This time, it's your eyes that think you're moving while your ear knows that you're sitting still.

But why does this conflicting information have to make us feel so terrible?

Scientists aren't sure about that either, but they think that there's an evolutionary explanation.

You see, both fast moving vehicles and video recordings have only existed in the last couple of centuries, barely a blink in evolutionary time.

For most of our history, there just wasn't that much that could cause this kind of sensory mix-up.

Except for poisons.

And because poisons are not the best thing for survival, our bodies evolved a very direct but not very pleasant way to get rid of whatever we might have eaten that was causing the confusion.

This theory seems pretty reasonable, but it leaves a lot of things unexplained, like why women are more affected by motion sickness than men, or why passengers get more nauseous than drivers.

Another theory suggests that the cause may have more to do with the way some unfamiliar situations make it harder to maintain our natural body posture.

Studies have shown that being immersed in water or just changing your stance can greatly reduce the effects of motion sickness.

But, again, we don't really know what's going on.

We all do know some of the more common remedies for car queasiness—

looking at the horizon, chewing gum, taking over-the-counter pills—

but none of these are totally reliable, nor can they handle really intense motion sickness.

And sometimes, the stakes are far higher than just not being bored during a long car ride.

At NASA, where astronauts are hurled into space at 17,000 miles per hour, motion sickness is a serious problem.

So, in addition to researching the latest space-age technologies, NASA also spends a lot of time trying to figure out how to keep astronauts from vomiting up their carefully prepared space rations.

Much like understanding the mysteries of sleep or curing the common cold,

Motion sickness remains one of those seemingly simple problems that, despite amazing scientific progress, we still know very little about.

Perhaps one day, the exact cause of motion sickness will be found, and with it, a completely effective way to prevent it.

But that day is still on the horizon.