Anemia occurs when the level of red blood cells or hemoglobin in the blood is too low, which can cause fatigue and stress on organs. It can be caused by excessive red blood cell destruction, blood loss, or inadequate red blood cell production. Common causes include iron deficiency, blood loss, and inherited disorders like sickle cell anemia or thalassemia. Symptoms include paleness and fatigue. Diagnosis involves blood tests, and treatment depends on the underlying cause but may include iron supplements, blood transfusions, or medications.