There may be the following reasons for the symptoms of sore legs while sleeping: 1. The most common reason is overworking of the legs. If excessive sports, especially competitive sports, excessive heavy physical labor, or long periods of immobility in the legs during the day, can cause fatigue and even injury to the leg muscles. When the soft tissues of the legs are fatigued, it proves that the leg muscles contract too many times, thus producing excessive and harmful metabolites, which can lead to sore legs; 2. If a patient suffering from a herniated lumbar disc, after the daytime work and study or labor, it is likely to make the herniated lumbar disc more serious. The protruding lumbar disc will stimulate the compression of the lumbar nerve, and trigger the symptoms of sore legs at night. This situation can be significantly relieved after proper rest; 3. If the legs are stimulated by cold, which triggers inflammation of the fascia of the legs, the symptoms of sore legs will also appear when sleeping.