How serious is it to have lumbar spinal stenosis?

Can be serious. Stenosis is an objective finding on imaging studies, like an mri. However the symptoms of lumbar stenosis determine how severe it is. It can be as mild as occasional pain or numbness radiating down the legs, to severe weakness, pain and numbness that worsens with walking. Depending on how severe the pain and disability is, determines the treatment.
Common problem. Lumbar spinal stenosis is a common problem especially for those older than 50. It can be managed conservatively in many patients for years. If surgery becomes necessary, it can be planned on an elective basis. Check out spine-health.Com.
Varies. It varies, some cases are mild and patients have minimal symptoms; in other cars patients can have severe pain and limited ability to stand and walk and can even lose control of their bowel and bladder.
Usually not . It can look a lot worse than what the symptoms are or even if there are no symptoms. You will have more than adequate warning from the stenosis in the lumbar spine before it can get really serious in terms of pain or neurologic symptoms and rarely neurologic findings.