I was listening to my body, but I misunderstood

I have been doing Range of Motion (ROM) exercises from the aforementioned book for the past week. When I first noticed that I had a problem with my knees, the backs of my knees were stiff.  Gradually over the past 2 years,  I noticed that I could not pivot, that it was increasingly more difficult to get up and down off the floor, that I was incredibly stiff in the mornings when I would first get up.  There were just too many ways that I noticed the stiffness in my knees which prevented me from doing what I wanted to do.  I thought that was my body telling me to cool it, give it a rest, this is the limit, you will pay if you keep this up, sister.  Then I read Dr. O'Neill's book where he says how important it is to do ROM exercises because the greater your ROM is before surgery, the better it will be after surgery.  Well, that motivated me, and I did the first exercise/stretch.  It was very uncomfortable, and I could not wait for it to be over.  I had a burning sensation and most of my left leg was very warm, even minutes after I finished the stretch.  My left knee is not only stiff, but it also had numbness in the back of the knee.  About 3 inches above the knee and 2 inches below the knee is numb.  The next day I repeated the exercise with less discomfort and less warm sensations along the leg.  Several days later, I am able to straighten my legs in ways that I thought were impossible.  Not only that, I would say that the numbness is about 75% improved. (Do you know how weird if feels to shave your leg and not feel it?  The razor would be cruising along, and then all of a sudden, it felt like it entered a dead zone and then the pressure of the razor reappeared again!)  Here is a picture of Passive Extension. 

Looks simple enough, but it is almost impossible to relax your stiff joint to go into as straight a position as possible.  Then after your muscles relax, you must "fire" or tighten up your quad muscles while you are pulling your knee downward and hold for 5 seconds. This is not a pleasant stretch, but I am already reaping benefits.  Dr. O'Neill states that this is the most important stretch to do during the first two weeks after surgery. He says to do it 15 minutes of every hour.  Hope I have lots of pain meds!