Doctor said that ablation procedure could result in me being a cripple dont wish to take the chance How do they determine what nerve to burn?

My spinal facet nerves L3-5 bilaterally (vertebrae are fused from DDD) ablations were done 2 1/2 weeks ago. I am having much less pain, which I love! There are spells of the bad pain where my back feels hopeless and seizes in agony like before. However I have had a full night of sleep. Amazing! So hope that this just means everything is settling down. I haven’t taken up my exercise so should call a physio.
I think that will be required by the Pain Clinic. Supposed to have some exercises regime.

The first ablation felt like a sunburn inside for about 3-4 weeks and then the whole area and the pain that I had before went numb. It was really nice for about a year and a half. Other pains in my back seemed to pop up since I have multiple problems but that really bad pain went almost completely away.
This 2nd ablation I just got like 2 months ago, either isn’t quite as effective or my pain is worse, or… im just not at that same comfort level. maybe only 50% numb.