The reason why the left side of the waist does not hurt when sleeping down does not hurt when sleeping down may be related to lumbar muscle strain, lumbar disc herniation, osteophytes and other conditions. 1. Lumbar muscle strain: long-term or high-intensity left side of the lumbar muscle overactivity, muscle tension is not promptly relieved, it will lead to lumbar muscle strain, sleep down the muscle briefly and effectively get relaxed, relieve pain, so there will be a left waist sleep down without pain without sleeping on the symptoms of pain. 2. Lumbar disc herniation: the nucleus pulposus of the lumbar intervertebral disc protrudes under the action of external forces, leading to compression of the adjacent spinal nerve roots around the left side of the nerve pressure is severe, there will be the symptom of the left side of the waist pain, sleep down when the lumbar spine is relatively reduced, the pressure and stimulation of the nerve roots to reduce. As a result, there will also be the performance of the left side of the waist sleeping down without pain without sleeping on the performance of pain. 3. osteophytes: lumbar spine osteophytes can cause lumbar spine around the fascia and soft tissue pressure, when the left side of the lumbar back of the fascia or soft tissue pressure is serious, then there will be a left side of the symptoms of lumbar pain, in the sleep of the lumbar activities to reduce the symptom will be alleviated, so there is a left side of the lumbar sleep down on the performance of the pain does not sleep on the performance of the pain. The left side of the waist to sleep down on the pain not sleep on the pain may also have other reasons, including scoliosis, etc. It is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.