I was riding my bike last week and I experienced something similar to your healing feeling with your kidneys... except that it was in my uterine.
Well, before leaving I felt pain in my uterine and I thought, exercise is precisely what I need. After riding the bike for about 15 minutes I felt better and then I had this feeling... hard to describe, it was like a firework. It was some sort of a warm feeling but very localized and then spreading like a firework here and there sparklings all over... what a strange feeling, but it felt great!