Possible causes of sudden back pain include strained back muscles, lumbar and dorsal muscular fasciitis, ankylosing spondylitis, etc. 1. Back muscle strain: It may be due to sudden bending, sudden turning, lifting heavy objects, resulting in back muscle strain, leading to sudden pain in the back. 2. Lumbar back muscular fasciitis: it may be related to long-term incorrect posture such as sitting and standing for a long time, which causes strain on the muscles of the lumbar back, leading to lumbar back muscular fasciitis. 3. Ankylosing spondylitis: In the early stage of ankylosing spondylitis, patients may have dull pain in the back or lumbosacral region, i.e., sudden pain in the back, which is alleviated by activities, and is obvious when waking up in the morning. Sudden back pain may also have other causes, 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.