Does your headache warrant a trip to the ER or just an aspirin and a nap? Knowing when it's actually appropriate to call a doctor, or maybe rush to the hospital, can be doubly useful: It lets worriers rest easy and prods those with serious symptoms to take action. The Harvard Medical School Family Health Guide and its editor in chief, Anthony L. Komaroff, MD, help you decode your pain.

• Headache: Tension or tumor?
• Chest pain: Heartburn or heart attack?
• Abdominal pain: Allergy or appendicitis?
• Dizziness: High blood pressure or low blood sugar?