Weakness and lightness after the reduction of fever mainly include the following causes: 1, lack of body fluids: fever will sweat a lot, resulting in a lack of body fluids, people will feel weak and light; 2, electrolyte disorders: sweating causes a lack of electrolytes in body fluids, causing electrolyte disorders in the blood, which may be manifested as low potassium, low calcium, making people feel weak and light; 3, energy consumption: due to the consumption of energy, the body mass decreases, which will The symptoms of weakness and lightness will be caused by energy consumption; 4. Weakness of resistance: these diseases that cause fever have certain damage to the body, and the organism will show symptoms of weakness and lightness because of the damage of these diseases; 5. The effect of drugs: some drugs taken during the treatment of fever will produce symptoms of weakness and lightness. Therefore, when the fever appears and the whole body is weak and light, we must pay attention to replenish body fluids, energy and vitamins to recover physical energy as fast as possible, which can better relieve the symptoms of weakness and lightness.