If lately you can't make it through the day without a power nap, it may be a sign of something more serious than sleepiness.

Marilyn Worthington, a real estate agent in St. Peters, Mo., remembers dragging herself through each day. "I was tired most of the time and needed to rest a lot," recalls Worthington, who at first attributed her fatigue to a hereditary kidney problem and didn't even mention the symptom to her doctor.

Fortunately, Worthington's doctor tested her for anemia, a condition that affects almost 3.5 million Americans. The test revealed that she was anemic. Now with the help of medication, Worthington is wide-awake and healthy again.

While fatigue is one side effect, anemia can lead to more serious health problems. To begin with, anemia results in less oxygen making it to the heart. This causes the heart to work harder to deliver oxygen in the form of red blood cells to the body.

"Over time, the heart muscle starts to enlarge and thicken," explains Dr. Allen Nissenson, co-chair of the National Anemia Action Campaign. "If that happens to your biceps, it's good. But if it is your heart, that's bad. Eventually the heart will not be able to continue to function adequately. It could lead to a potentially fatal heart condition."

Symptoms of anemia include lethargy, fatigue, rapid heartbeat, high blood pressure, shortness of breath, paleness, increased irritability, loss of concentration, dizziness, fainting and insomnia.

Those at greatest risk for anemia include women who have heavy menstrual periods that could result in an iron deficiency. Nissenson believes that millions of people with anemia are undiagnosed. He urges those at risk to receive periodic blood tests.

If you are a woman of child-bearing age or have any of the conditions that might predispose you to anemia including kidney disease, AIDS, rheumatoid arthritis, or have undergone surgery during which you lost a significant amount of blood, ask your doctor to order a complete blood-count test (CBC) at your next physical exam.

If you find that your iron is low, you may need nutritional supplements to produce red blood cells. An alternative would be to add iron-rich foods to your diet, like wheatgrass juice.

Although fatigue is a common symptom of anemia, just because you're tired doesn't mean you're anemic. "Everyone is fatigued," says Nissenson. "The issue is to increase doctors' awareness that even something as vague as fatigue could be a sign of anemia."