Thanks for your responses, David and Barbara. (Barbara, your input is quite welcome--I was a Protestant myself until barely a few months ago, so I know they can think clearly and offer valuable opinions!) I think it's probably true that the best way up is down, because the most dramatic answers to prayer I've experienced occured after I was on my knees in tears.
David, LOL, I think my first experience of prostration actually on the floor will probably be my last! With my replaced knee still limited in mobility and my other knee not in great shape, it looked for a while that getting up again was quite impossible. Eventually I managed to get back up, but I've decided maybe I should compromise and lay on my bed, a much safer proposition.
Good news, speaking of prayer positions! Finally, finally, I can kneel at Mass or during Adoration for pretty good stretches of time, and I'm so happy because everyone I asked who had had the replacement said I would never be capable of kneeling again.
What is it about prostration that makes it so different? Is it the humility of it? Also, so many customs in the Church have their roots in Hebrew practices. Was prostration known commonly in the ancient Hebrew faith? I remember that David prayed prostrate on the floor as his child was dying, but was that an isolated thing?