The common symptoms of severe anemia include fatigue, shortness of breath, palpitation, and angina and fainting in some patients. 1. Weakness, palpitation, shortness of breath: hemoglobin of patients with severe anemia is lower than 60g/L, which can directly lead to the reduction of oxygen-carrying capacity of hemoglobin, thus leading to tissue ischemia and hypoxia caused by the above symptoms. 2. Ischemic heart disease: insufficient oxygen-carrying capacity of hemoglobin leads to ischemic and hypoxic heart disease, which is manifested as accelerated heart rate and angina. 3. Fainting: Insufficient oxygen-carrying capacity of hemoglobin directly leads to insufficient blood supply to the brain, which is manifested by abnormal brain function, such as headache, dizziness, fainting, etc. Severe anemia is often caused by acute blood loss. Severe anemia is mostly due to acute blood loss, hemolytic anemia, aplastic anemia, etc., which can be life-threatening in severe cases. If symptoms such as weakness, dizziness, palpitation, shortness of breath, etc. occur, attention should be paid to them, and they should go to the hospital in time for consultation and treatment.