Severe fatigue. When anemia is severe enough, you may be so tired that you can't complete everyday tasks. You may be too exhausted to work or play.
Heart problems. Anemia can lead to a rapid or irregular heartbeat - an arrhythmia. Your heart must pump more blood to compensate for the lack of oxygen in the blood when you're anemic. This can even lead to congestive heart failure.
Death. Some inherited anemias, such as sickle cell anemia, can be serious and lead to life-threatening complications. Losing a lot of blood quickly results in acute, severe anemia and can be fatal.