If you get nauseous in cars or queasy on planes, don’t worry — your body just thinks it’s being poisoned.

That’s according to National Geographic, which says your brain is confused because you are sending it mixed signals. It sure seems like you’re moving … but it also doesn’t.

Read: Does Losing Sleep Really Make You Sick?

“This whole mix-up is basically the result of evolution not catching up to technology,” National Geographic video host Angeli Gabriel says. “Cars, boats, trains — they haven’t been around long enough for our brains to adapt. … Unlike walking, which we’ve had millions of years to adapt to.”

The feeling of moving but not moving makes your brain think something toxic is destroying your nerve tissue, also known as being poisoned. Nausea and possibly clearing your body through vomiting is how it responds.

Motion sickness is not the only type of ailment that results from your brain or your body getting confused. Extreme allergic reactions that throw people into anaphylactic shock, a potentially deadly condition, occur when your immune system identifies harmless substances as dangerous invaders and pulls out all the stops to attack them.

See also:

5 Deadly Poisons That Are Also Medicine

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