Nausea is that queasy, uncomfortable feeling in your stomach when you think you might throw up. Your stomach churns, your mouth might water strangely, and you feel like everything inside you wants to come up. You might feel nauseated after spinning too fast on a merry-go-round, riding in a car on a winding mountain road, or when you have the stomach flu.

Sailors have battled nausea for thousands of years as their ships rock on ocean waves. That rolling, unstable feeling can make your stomach revolt even when you're perfectly healthy otherwise.

Nausea doesn't always lead to vomiting. Sometimes it passes after you rest, breathe fresh air, or drink something cold. Other times it's your body's way of warning you that something is wrong: spoiled food, illness, or too much motion. Some people feel nauseated when they're extremely nervous, like before a big performance.

When something makes you feel nauseated, you can say it's nauseating. A disgusting smell might be nauseating, or watching someone eat something gross. The feeling of nausea is miserable, but it usually means your body is trying to protect itself from something harmful.