Musculoskeletal strain: This is often the most common cause of back pain, including pain that occurs or worsens at night. It can be due to poor posture, overuse, or direct injury to the muscles and ligaments in the back.

Herniated disc: A herniated disc can cause back pain that worsens at night, especially if the disc is pressing on a nerve. The pain can radiate down the legs and may be accompanied by numbness or tingling.
Degenerative disc disease: As discs degenerate, they can cause chronic back pain that may worsen at night due to the lack of activity and the body's position during sleep.
Scoliosis: Although often diagnosed in childhood, scoliosis can cause back pain in adults, especially if the curvature worsens over time. Night pain can occur due to the abnormal spinal alignment.
Osteoarthritis: Spinal osteoarthritis can lead to back pain that is worse at night due to the inflammation and stiffness in the spinal joints.

Cancer: Although rare, cancer (such as multiple myeloma or metastatic disease to the spine) can cause night pain due to the destruction of bone tissue. It's crucial to consider this diagnosis, especially in patients with a history of cancer or unexplained weight loss.
Infection (osteomyelitis, discitis): Infections of the spine can cause severe back pain that worsens at night. These conditions are medical emergencies and require prompt treatment.
Fracture: Osteoporotic fractures or traumatic fractures can cause back pain that worsens at night. In patients with osteoporosis or those on long-term corticosteroid therapy, even minor trauma can lead to a fracture.
Spinal stenosis: This condition involves narrowing of the spinal canal, which can cause back pain, especially when lying down or at night, due to the increased pressure on the nerves.

Paget's disease of bone: A chronic condition that can result in enlarged and misshapen bones, leading to back pain that may worsen at night due to bone deformities and nerve compression.
Ehlers-Danlos syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. It can lead to musculoskeletal pain, including back pain at night, due to joint hypermobility and tissue fragility.
Spondylolisthesis: A condition where one of the vertebrae slips forward over the bone below it, which can cause back pain that worsens at night, especially if it leads to nerve compression or spinal instability.