According to Catholicism, what did St Paul mean by "a thorn in the flesh"?

We see St Paul writing at 2 Corinthians 12:7 (RSVCE): > And to keep me from being too elated by the abundance of revelations, a thorn was given me in the flesh, a messenger of Satan, to harass me, to keep me from being too elated. What exactly was St. Paul referring to here? Was he telling an idiom of his time in order to show that he was undergoing some painful medical condition? Or, was he referring to the temptations of flesh? Are there any authentic interpretations from the side of Catholic Church on the saying of St Paul?