Two things:
- The Placebo Effect: The effect that if you are given something that you think will have an effect on you, it will have that efect to a degree. Did you know that if you give people something that tastes of alcohol and tell them it's beer, they'll get drunk, even if there's no alcohol in it whatsoever? I've experianced the placebo effect myself, so have lots of people, it's a documented and tested psychological phenominon. If you have enough faith that your prayer will stop your heart pains, then when you pray, your mind numbs itself. You got rid of the pain yourself, I'm afraid.
- We naturally remember our successes more than our failures. I was once briefly convinced that I could see the future, and when I excitedly gabbled this off to my mother, and she dryly asked me why, I said that I'd just predicted the song a TV host was going to put on. I then cited about five or six other incidents where I'd predicted as well. Mum then asked me to cite the times I hadn't predicted the future. I couldn't remember them, but thinking back on it now I'm older of course there were loads of cases before that moment where I'd guessed the future wrong. I wanted it to be true, so my mind provided all of the times I'd gotten it right- another documented psychological phenominon.
Now, if you wanted to convince me of God's healing, you'd do a few things. First, you'd cut your arm off. Then you'd pray, and God would reattach it/grow a new one for you. That kind of reparation that's well beyond human capacity and well beyond the capacity of the mind to pretend. That'd dismiss the placebo effect. Then you'd do this again, every night for a month, and tally the number of times God reattached it with the times God didn't (using other limbs for the time he didn't). That'd show that you actually had a decent number of successes in comparison to your failures.