When the elderly have no energy after recovering from a cold, it may be related to dehydration, poor diet and prolonged bed rest, etc. They can regain their strength by drinking more water, having a reasonable diet and increasing their activities appropriately. 1. Dehydration: During a cold, the elderly may be easily dehydrated due to fever and sweating. However, the gastrointestinal function is impaired during a cold, so the body may not be rehydrated in a timely manner, leaving the body in a dehydrated state, resulting in the symptom of lack of energy. It is recommended to drink more water and pay attention to rest to improve the symptoms. 2. Poor diet: During cold and flu, especially the elderly are prone to weakened gastrointestinal function, food is not easy to digest, and the duration of cold and flu in the elderly may be slightly prolonged, resulting in a long period of time to eat less, resulting in the recovery of cold and flu after the body has no strength. After recovering from a cold, it is recommended to eat a healthy and scientific diet, rich in high quality proteins and vitamins and other foods to replenish nutrients. 3. Prolonged bed rest: Older people may mainly stay in bed during cold and flu due to physical discomfort, resulting in weakness of lower limbs. It is recommended to gradually increase the activities of getting out of bed to gradually restore the strength of the lower limbs. Prolonged weakness of the whole body can also be caused by other diseases, not necessarily related to colds. If the symptoms do not improve or worsen, you should consult a doctor for scientific treatment in order to avoid delaying your condition.