Just a thought but I had both of my knees go numb several years ago...not just 'feeling numb'...really numb so if I pinched them I couldn't feel a thing. I was about to go to the doctor and it went away. It turns out I had been sleeping on my side with my knees pressed together and had compressed the nerves. I now put a pillow between them, but if I forget....NUMB and pain like you described below the knee...nerve pain. Don't know if that's what going on with you but that was my problem.