Such nonsense! Bipolar disorder is a physical brain disorder. It can be helped with drugs, and many people who are not Christian live normal lives with it, provided they stay on their meds. (And Christians, too!) And while people were afflicted in the Bible by demons, that is not the same as modern bipolar.
I run a bipolar group, some are Christians, some are atheist, Buddhist and we had a Muslim once for a while. The symptoms were all the same, because bipolar disorder is not spiritual. One woman is a very strong Christian. She is really bad, has to take lots of meds. But she befriends everyone in the forum, and witnesses to them. And prays for people. I feel sorry she has bipolar so badly, but she is content to be in a ministry not many people go into. I also stand up for Christ, although I am more there to keep things running smoothly.
The word translated as "sound mind" in the KJV is σωφρονισμοῦ in Greek. It is a hapax legomena, meaning it is only found one time in the Bible. Paul uses a cognate word in 1 Tim. 3:2, as "prudent, thoughtful, self-controlled." In fact, Paul uses this to describe in this context, a combination of the characteristics of prudence and self-discipline. While "sound mind" could be a use of the word, it does not fit the context of the chapter and book. It is not talking about mental illness, but rather that as Christians we have to have self control or discipline.* So try quoting a newer version, which uses modern language.
In fact, bipolar disorder is just another disease! God does heal, but not everyone. I find it hard to believe you were ever truly bipolar, probably borderline is more like it. But again, I am talking to you.
*George W. Knight III, The Pastoral Epistles, from the New International Greek Testament Commentary, Wm. B. Eerdmans Publishing, MI, 1992, 372.