There are many reasons for the lack of energy and fatigue, including cardiovascular diseases, diabetes mellitus, anemia, myasthenia gravis, renal diseases, liver diseases, and hypothyroidism. 1. Cardiovascular system diseases: such as heart failure, thromboembolic vasculitis, aortitis causes insufficient blood supply to the circulatory system, which may lead to fatigue. 2. Diabetes mellitus: the symptoms of “three more and one less”, such as eating more, drinking more, urinating more and losing weight, and the symptoms of fatigue due to the abnormality of blood glucose. 3. Anemia: the ability of blood to carry oxygen decreases, resulting in fatigue. 4. Myasthenia gravis: Myasthenia gravis can cause fatigue, and the fatigue is often light in the morning and heavy in the evening. 5. Kidney disease: renal impairment may lead to hypoproteinemia, hypokalemia, etc., which may cause fatigue. 6. Liver disease: such as liver failure can cause insufficient energy intake, resulting in generalized nutritional disorders and fatigue. 7. Hypothyroidism: hypothyroidism is characterized by insufficient thyroid hormones, which can lead to fatigue. There may be other reasons for the lack of energy and fatigue, and it is recommended to consult a doctor in time to clarify the cause of the disease and avoid delays.