Since I have Epilepsy, I always wanted it to be Epilepsy myself. Anybody that has the proverbial thorn in their flesh but still makes you stronger spiritually, believe whatever you want when it comes to that!
We don’t believe in religious relativism, as in, anything goes, as truth. There are definite truths within the whole Truth.
What you say about things making us stronger, is true. All things can sanctify us. ‘Stronger’, in this sense, is to learn that we have to rely on our Creator completely, and not on our…selves.
Our Creator does not give thorns of suffering but does allow for them, and in some cases, these manifest as holy signs for the good of the faithful, after those chosen, give their assent (in the cases of saints, for example). And in the case of St. Paul, his thorn chipped away at his pride. It was a personal thorn that was eventually included for us in Scripture. But he did not know why he had it, at first. We know this because he asked for it to be gone. And we know it was an infliction brought on by a demon. Epilepsy, on the other hand, brought on by diabolical activity, is rare, as possession is rare. And I don’t believe St. Paul was possessed by an evil spirit! Epilepsy, otherwise, is a natural sickness. But his thorn would have been more along the lines of
demonic oppression. So, epilepsy is not likely, as demons are not natural occurrences and neither are their oppressive tendencies; rather, they are supernatural.
We can estimate that the demon must have been allowed only after St. Paul’s conversion because demons manifest in a more obvious way as the soul moves closer to Heaven. Again, pointing to an affliction of external temptations.