When John of God was 42 years old, he attended a sermon by St. John of Ávila that produced, in him, a violent reaction. The sermon's subject was one's being made a fool for the sake of Jesus, and afterward John ran into the street, rolled in the mud, and beat himself, begging mercy for his sins.
An orphan since age 8, he had spent two decades as an enlisted soldier fighting across Europe. For this public display of lunacy, he was locked in prison. Word eventually reached John of Ávila. John of Ávila visited John of God and deduced that he was quite sane, albeit consumed with a guilt that could be overcome by serving others. Realizing this, too, John of God came to his senses and was soon let free, after which he founded a hospital and entire Hospitaller Society to care for the poor and ill.
Fifteen years later, on March 8, 1550, John of God died from pneumonia he'd caught it in the course of saving a drowning stranger from a cold river.