Musculoskeletal Strain: This is the most common cause of sudden onset lower back pain, often resulting from lifting heavy objects, sudden movements, or minor trauma. The pain is typically localized to the lower back and may radiate to the buttocks or thighs.

Herniated Disc: A herniated disc can cause sudden onset lower back pain, especially if it compresses a nerve root. The pain may radiate down the leg and be accompanied by numbness, tingling, or weakness.
Degenerative Disc Disease: This condition can cause sudden onset lower back pain, especially if there is a sudden exacerbation of the degenerative process.
Spondylosis: This condition, characterized by a defect in the pars interarticularis, can cause sudden onset lower back pain, especially in young athletes.

Cauda Equina Syndrome: A serious condition that requires immediate medical attention, characterized by severe lower back pain, numbness, tingling, or weakness in the legs, and loss of bladder or bowel control.
Spinal Infection (e.g., Osteomyelitis, Discitis): Infections of the spine can cause sudden onset lower back pain, fever, and other systemic symptoms.
Spinal Fracture: A fracture of the spine can cause sudden onset lower back pain, especially if it is related to trauma or osteoporosis.
Abdominal Aortic Aneurysm: A ruptured abdominal aortic aneurysm can cause sudden onset lower back pain, abdominal pain, and other systemic symptoms.

Spinal Tumor: A tumor of the spine can cause sudden onset lower back pain, especially if it compresses a nerve root or causes spinal instability.
Paget's Disease: A rare condition characterized by abnormal bone remodeling, which can cause sudden onset lower back pain and other systemic symptoms.
Osteonecrosis of the Spine: A rare condition characterized by the death of bone tissue in the spine, which can cause sudden onset lower back pain and other systemic symptoms.