About Anemia Many people with chronic (long-term) illnesses, such as cancer, HIV infection, or renal disease, have a lack of energy or tire easily. There are many possible reasons for this type of feeling, but a common cause is a condition called anemia. Red blood cells (also called erythrocytes) carry oxygen from your lungs to the rest of your body. Anemia is a condition in which there is a shortage of red blood cells circulating in your body. A person with anemia may have any of the following problems: Weakness or fatigue Shortness of breath  Loss of stamina  Rapid heart rate  Pale skin  Pounding headaches  Heart palpitations Since these problems may be caused by conditions other than anemia, health care professionals can order tests to study a patient’s red blood cells and determine if anemia is the cause of these symptoms.