What's the worst physical pain you've ever experienced?

If I had to guess I would say probably when I pulled a muscle in my back while fencing. I did what many people sarcastically call "the parry 9" while fencing someone and the guy I was fencing instead of letting up kept pushing me until I was bent in a very unnatural position. I ended up with a pulled back muscle which was awful for the few days I was afflicted with it.