What could a very large knot on the left-center of extreme lower back be that is painful and came up over night?

There are a few possible causes for a very large, painful knot that suddenly appears on the left-center of the extreme lower back. Some potential causes include:

1. Muscle Spasm: A muscle spasm is an involuntary contraction of one or more muscles. It can cause a knot-like feeling in the affected area and can be very painful. Muscle spasms in the lower back can be caused by various factors, such as strain or injury, poor posture, or dehydration.

2. Herniated Disc: A herniated disc is a condition in which the soft, inner portion of the spinal disc protrudes or ruptures through a weakness in the outer layer of the disc. This can cause pain, numbness, or weakness in the areas near the affected nerve. If a herniated disc occurs in the lower back, it could lead to a knot-like bulge and significant pain.

3. Spinal Stenosis: Spinal stenosis refers to the narrowing of the spinal canal, which can put pressure on the spinal cord and nerves. It commonly affects the lower back and can cause various symptoms, including pain, numbness, and muscle weakness. A knot-like feeling in the lower back could be associated with spinal stenosis, particularly if accompanied by other symptoms like pain radiating down the leg.

4. Kidney Issues: Sometimes, a large, painful knot in the lower back on the left side could indicate a problem with the left kidney. Kidney stones or other kidney-related issues can cause localized pain and discomfort in the lower back area.

5. Soft Tissue Injury: A sudden impact, fall, or injury to the lower back could lead to soft tissue damage, causing inflammation, swelling, and pain. This can result in a noticeable knot or lump in the affected area.

6. Abscess: In rare cases, a bacterial infection can lead to the formation of an abscess, which is a collection of pus. An abscess in the lower back could manifest as a painful, swollen knot.

7. Spondylolisthesis: This condition occurs when a vertebra in the spine slips forward, putting pressure on the nerve roots. Spondylolisthesis can lead to a painful knotting of the muscles in the lower back as the body attempts to stabilize the affected area.

It's important to note that without a proper medical assessment, it can be difficult to determine the exact cause of the knot. If the pain is severe or persistent, it's recommended to seek medical attention from a healthcare professional, such as a doctor or a physical therapist, to receive an accurate diagnosis and appropriate treatment.