Boy, I can relate to all you that just don't feel the energy like they used to.
I waited too long to get my knee replaced and when the surgeon replaced my knee 3 months ago, he said that I didn't have any cartilage left and that the arthritis was so severe that it wore my knee smooth. I plan on getting my other one replaced in about 4 months. Although the new knee to doing fairly well, the other one is really holding me back a great deal.
Then I started thinking about how long that my knees have been hurting me and realized that it has been about ten years. Over that ten years I have done less and less and now I find that I not only have to exercise to help the new knee get better, but I also have to exercise to get my wind back up. Being sedentary has left me rather breathless and I get winded just walking a block. I also realized how small my world has become.
The moral of the story is if you need to have knee replacements, don't hesitate. I found that the amount of pain post surgery wasn't any greater than the pain I was enduring before the surgery. But, the best part was that as the weeks have gone by the pain has lessened to the point of non-existence in the knee that had surgery. I think of all of the things that I have stopped doing because of knee pain and I really regret not getting it done when the surgeon first mentioned it.