I'm sure by now you have learnt a lot about Ankylosing Spondilitis. In layman terms one can describe it as a condition affecting the joints of the spine by bridging new bone between them. This hampers flexibility hence restricts the range of motion. Over a period one has to go through anti inflammatory, disease modifying medications along with exercises and physiotherapy.
You might be having pain relapses once in a while. It may be related to unaccustomed activity or posture. So I would advise you to take rest and improve posture till the pain subsides. The trick is not to do things that you fear would aggravate your symptoms, like excessive walking, working out, or twisting back etc. You seem to have relief in forward bending which stretches your paraspinal muscles and relieves muscle spasm.
The new bone formation if extends into the spinal canal may lead to stenosis. The pressure is exerted on either the cord itself or the traversing or exiting spinal nerve. If you have symptoms like tingling numbness in one/both legs or pain radiating from behind your thighs up to toes, then lumbar canal stenosis is a possibility.
Meanwhile, till you see your rheumatologist, refrain from any major physical activity, take adequate rest and use hot fomentation. Use medications under your physician’s guidance.
Hope that this information helps and hope that you will get better soon.
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Dr. Atul Wankhede