According to Yahoo News today, a new book by Monsignor Slawomir Oder claims that Pope John Paul II habitually abused himself:
John Paul frequently denied himself food — especially during the holy season of Lent — and “frequently spent the night on the bare floor,” messing up his bed in the morning so he wouldn’t draw attention to his act of penitence.
“But it wasn’t limited to this. As some members of his close entourage in Poland and in the Vatican were able to hear with their own ears, John Paul flagellated himself. In his armoire, amid all the vestments and hanging on a hanger, was a belt which he used as a whip and which he always brought to Castel Gandolfo,” the papal retreat where John Paul vacationed each summer.
Prometheus Unbound 