MINNEAPOLIS (WCCO) — Hundreds of thousands of people will spend part of their summer vacation on amusement park rides. North America has more than 600 roller coasters and people ride them more than two billion times every year.

Thinking about being on a roller coaster right now? You know the feeling.

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“Like your hearts up here and you’re down here,” said one rider at Nickelodeon Universe inside Mall of America.

“You feel like your stomach’s floating in your chest,” said another.

So what’s happening, medically, when it feels like your stomach drops on a roller coaster?

“The honest answer is that no one knows with absolute certainty,” said Dr. Brad Sagura, a surgeon at University of Minnesota’s Amplatz Children’s Hospital.

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“There’s a cast network of nerve connections within the body, handling messages between the spinal cord, the brain and other structures,” Sagura said.

When you hit the peak of a roller coaster and start dropping so quickly, things inside start to shift around.

“The liver and spleen are relatively secured by suspensory ligaments,” Sagura said. “But the intestines themselves are relatively mobile. While your body is secured by your seat belt, the organs are free to move about by some extent. That contributes to the free-fall floating sensation that either calls us back for more, or has us running to get sick from nausea.”

The movement isn’t only the movement of the organs, it is also the movement of what’s inside the organs.

“The intestines, the stomach, they hold liquid,” Sagura said. “The bladder; the same thing. “It’s relatively fixed, but the fluid within those structures probably plays a role in that sudden drop.”

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Sagura said there’s no long-term danger from your organs slightly shifting around. They go back to where they started. But the movement is enough for your nerves to notice that something’s happening, he said.

Jason DeRusha