Severe leg pain and stiffness after sleeping in front of a cooler can occur due to muscle spasm, cold exposure, poor sleeping posture, nerve irritation, or sudden nighttime muscle tightening. Cold air may sometimes increase muscle stiffness and body pain, especially in people who already have muscle weakness, vitamin deficiency, joint problems, or poor circulation. Pain-relieving medicines, warm compresses, gentle stretching, light massage, and keeping the legs warm may help reduce stiffness and improve comfort gradually. Adequate hydration, proper sleep, and avoiding direct exposure to cold air at night may also help prevent the muscles from tightening further. Resting the legs for a short time while still doing gentle movement may improve recovery better than complete bed rest. Swelling, redness, numbness, severe weakness, fever, or pain spreading from the back down the leg can sometimes suggest nerve irritation, circulation problems, or deeper muscle inflammation and may need further evaluation and treatment.