Knee Theories

So I have some theories about my knee. It seems odd that for my whole athletic life, I didn't experience knee pain, and now suddenly it's the main source of trouble for me. And this is knee pain that is really just a ligament thing, like my leg was hyperextended or something. Basically, stretching pain, not pounding pain. And the other day, I remembered that time almost 10 years ago when I fell down the stairs and my knee bent under me as I fell on it with all my weight. I did hyperextend it, just not past straight. Past bent. I remember at the time I was in so much pain I thought I broke my leg. Needless to say, I never went to the doctor because I had no insurance (funny how nothing changes), and just let it heal on its own and then forgot about it. Is it possible that this is that same injury? How do I fix it? Can I even do that, or is this going to be something that plagues me forever? It's kind of a bummer, because it's really scary to feel like my leg might give out on my when I really need it. Anyway, I'm really bummed that it ever happened and is now coming back again. Blech. I hate getting old.