Innumerable individuals throughout history have become ill and then have recovered illustrating the common grace of God:

[Mt 5:45b]:

'For He causes His sun to rise on the evil and the good, and sends rain on the righteous and the unrighteous."

The vast majority of them were not Christian, but instead were of other faiths - worshipers of demonic god(s), rejecting our Lord's sacrifice for them on the cross. Therefore they never did pray properly to the one true God, yet they were completely healed.