If the patient feels sore in the thighs after sleeping, it may be caused by the following reasons: 1. It may be caused by excessive fatigue, if the patient did too intense activities in the first day, resulting in a large amount of lactic acid deposition inside the muscles, it is very likely to cause the patient to wake up the next day with soreness around the thighs. 2. It may be caused by some bad posture. If the patient has a bad sleeping posture during sleep, so that the muscles in a certain part of the thigh are in spasm for a long time, when the patient wakes up the next day, there may be localized soreness. 3, it may be caused by cold. If the patient sleeps at night, the thigh area has cold, it may cause the patient to feel around the obvious soreness in the next day. 4, may be caused by long-term pressure. If the patient inadvertently presses a certain position of the thigh for a long time while sleeping, it will cause insufficient blood circulation in the area, and the patient will wake up the next day with obvious soreness in this area.