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Pain worsens at rest

The acid that is supposed to stay in your stomach is more likely to escape into your esophagus when you lie down or bend over, causing heartburn.

"If you're sitting up straight, gravity helps keep food in the stomach," says Dr. Coyle. "If you lose the gravity, you're more prone to reflux."

That's why people with chronic heartburn raise the head of their bed, and why they shouldn't eat big meals right before bedtime.

Next: Post-meal pain