Hi I am 76 years old,weigh 80KG have been active in Karate for last 20 years,10 years ago I tore the Sciatic nerve at the root source and spent three months on my stomach but came right after that.Just recently (last week) I was kneeling down and when I stood up I experienced an excrusciating pain in the lower back that made me collapse to my knees,since then it happens for no reason combined with acute knee pain,it seems as if when I have been standing for long periods it happens more frequently,can you help?Thanks, Mike.