Adam Clarke on Galatians 4:13

Ye know how through infirmity - The apostle seems to say that he was much afflicted in body when he first preached the Gospel to them. And is this any strange thing, that a minister, so laborious as St. Paul was, should be sometimes overdone and overcome by the severity of his labors? Surely not. This might have been only an occasional affliction, while laboring in that part of Asia Minor; and not a continual and incurable infirmity, as some have too hastily conjectured.