In one sentence, describe what the following article is about:

Heart palpitations, chest pains, and severe abdominal pain are all signs of a serious allergic reaction. If you're experiencing any of these symptoms, stay calm. You may be experiencing a reaction that could be anaphylaxis. Get immediate treatment to avoid life-threatening symptoms such as anaphylactic shock or a heart attack. Focus on your breathing to help calm yourself down and make sure you're getting enough oxygen. If you think you may be having a heart attack, call emergency medical services immediately. Some discomfort, nausea, or even diarrhea after you eat something could just be a harmless effect of eating food that was maybe too spicy, greasy, or heavy. However, if you experience extreme nausea, vomiting, or diarrhea that won't go away after a few hours, you may be having a serious gastrointestinal reaction that needs to be checked out by a doctor to make sure it's not dangerous. Nausea, vomiting, or diarrhea could be a sign of a more serious systemic allergic reaction. Call your doctor if you're still experiencing serious symptoms 3 hours after you eat. They may ask you to seek emergency treatment. A serious allergic reaction can cause a major drop in blood pressure, which can cause you to feel disoriented or extremely anxious. If you suddenly find yourself lost and confused, or your heart is beating fast and you have anxiety, you may be experiencing the onset of a serious reaction. Pay attention for any other potential symptoms that could confirm that you need immediate medical attention. Sometimes a serious reaction caused by a food allergy can take time to affect your whole system, and your blood pressure may be affected first, which could cause you to feel anxious and confused, but otherwise normal. Keep an eye out for additional symptoms.

Summary:
Check for pain or tightness in your chest or abdomen. Pay attention to nausea, vomiting, or diarrhea after you eat. Take note if you suddenly feel confused or anxious after eating.