You wake up in the middle of the night with severe chest pain.

Your first thought: Am I having a heart attack?

But experts say another common condition — gastroesophageal reflux disease (GERD), or chronic acid reflux — can cause symptoms that closely resemble a heart attack.

So how can you tell the difference?

GERD is a chronic digestive condition in which stomach acid repeatedly flows back into the esophagus, the tube that connects the mouth to the stomach. This acid reflux irritates the lining of the esophagus, causing the burning chest pain commonly known as heartburn.

A heart attack, or myocardial infarction, occurs when blood flow to part of the heart muscle is suddenly blocked, usually by a blood clot that forms on a ruptured fatty plaque in a coronary artery. Without prompt treatment, the affected heart muscle begins to die.

Heartburn is extremely common. About 60 million Americans experience it at least once a month, and up to 15 million have symptoms every day, according to the National Institutes of Health.

Heart attacks are also common. About 805,000 Americans have a heart attack each year — roughly one every 40 seconds — according to the Centers for Disease Control and Prevention.

Because both conditions can cause chest discomfort, it's not always easy to tell them apart. The safest rule is this: If your chest pain is new, severe, unusual, or you're not sure what's causing it, treat it as a possible heart attack and call 911 immediately.

According to the Mayo Clinic, these symptoms may help distinguish the two conditions.

Typical Signs of Heartburn or GERD

• Burning pain behind the breastbone or in the upper abdomen
• Symptoms that usually occur after eating or while lying down or bending over
• A sour or bitter taste in the mouth
• Symptoms that may improve with antacids
• Burping, bloating, or regurgitation

Typical Signs of a Heart Attack

• Pressure, squeezing, fullness, or pain in the chest
• Pain that spreads to the arm, shoulder, back, neck, jaw, or upper abdomen
• Shortness of breath
• Sweating, nausea, vomiting, dizziness, or fainting
• Unusual fatigue or lightheadedness
• Symptoms triggered by physical exertion or emotional stress
• Symptoms that do not improve with rest or antacids

Women may experience heart attack symptoms differently than men, according to UC Davis Health. About 40% of women who have had a heart attack reported heartburn-like symptoms shortly before the event. Women are also more likely to experience nausea and vomiting along with other heart attack symptoms.

Women over age 50 who develop these symptoms — especially if they have risk factors such as diabetes, obesity, high blood pressure, high cholesterol, or a family history of heart disease — should seek emergency medical care right away.

When it comes to chest pain, it's always better to err on the side of caution. If you think you may be having a heart attack, don't try to diagnose yourself or drive to the hospital. Call 911 immediately so treatment can begin as quickly as possible.