When I first heard St. Paul speak of his "Thorn in my flesh" my first understanding of it was some sexual torment. Maybe I was interpreting it with my own eyes and weaknesses.
I don't think any of us know. He doesn't really say. But he speaks in this context of being beaten. I have wondered if he had experiences like Padre Pio. Demonic beatings. Some saints have been afflicted with this so its very possible.
Father Mike in the video says that sometimes God leaves us our thorn or weakness to keep us humble. I definitely agree on that point. Makes me feel a little better knowing there is a reason for my weakness.
The most common explanation I have heard for the thorn was that St Paul had some kind of problem with his eyes. They justify this diagnosis by referring to other scripture (maybe as result of multiple beatings and stonings?). Galatians 6:11 11 See what large letters I use as I write to you with my own hand! But no one really knows and everyone has fun guessing. I used to think quite a lot about this verse because of something that happened with my Spiritual Director. He suggested to me that Paul's thorn in the side was a sexual problem. Years and years later we were talking about this verse and he asked me what I thought the thorn might be. I said I thought it might be a sexual problem. His jaw dropped open and he was totally horrified. 'Where ', he asked in shocked tones, 'Did you ever hear such a horrible thing, he was a saint!!' 'From yourself', I replied. He was so shocked he could not speak for a while. Then he vehemently denied it. But I know he did say it , it stuck in my mind and heart. But I did not argue. I think something like this verse we are inclined to interpret it from our own perspective. It's really an open question but we each interpret in our own lights at the time.
Since St Paul also writes: "I bear the marks of Jesus in my body" Perhaps the thorn is the stigmata. Or perhaps the stigmata accompanied by physical torments and temptations by a fallen angel...just as AED wrote and Padre Pio experienced.