In-depth

Risk factors

Depression

Symptoms

Fatigue

Headache

Most headaches aren't caused by a serious illness, but some could be a sign of a life-threatening condition.

Nausea and vomiting

Tachycardia

Tachycardia, a rapid heart rate, is caused by an abnormality in your heart's electrical impulses. Tachycardia can cause serious complications, including sudden cardiac arrest.

Dec. 20, 2014