Back pain when sleeping, but no pain during the day can be seen in the following cases: 1, the bed is not suitable: for example, sleeping in a very soft bed, when sleeping, the spine will be sagging, the physiological curvature of the back will change, the back muscles are in a prolonged period of time in a state of tension will cause back pain at night; 2, orthopedic specific diseases: for example, ankylosing spondylitis, the time of the pain is mainly in the night, and many patients will be the back pain at night, or even waking up with the pain. Ankylosing spondylitis patients should go to the hospital for blood HLA-B27 test, but also for bilateral sacroiliac joints of the orthogonal oblique X-ray, in order to clarify the diagnosis.