I have a Crystal Ruby "red dragon" that used to do the same thing every couple months when I would do water changes. I thought he was destined to death every time, I would move him into quarantine and dose with Pazipro and aquarium salt and after about a day he would be back to his old self. He is still kicking (Flipping?) and to this day have never found the underlying cause.. Not going to say that is the correct or best treatment, But in regards to that specific fish has worked for me.