Soreness in the feet in the middle of the night can be a result of nerve irritation caused by poor blood circulation due to pressure on local muscles caused by improper sleeping posture, or it can be caused by a condition such as a herniated disc in the lumbar spine. If this symptom persists for a long time and the patient also suffers from symptoms such as lumbar pain and radiating pain in the lower limbs, he/she needs to seek medical attention as soon as possible.