DY: Fasting is something separate from physically hurting oneself. We completely reject self-damaging just as we completely reject those Rishonim who were corporealists. We minimize fasting because of your Sevara. That’s not why we don’t beat ourselves.
newbee: It’s a “Tshuvah” in the Besamim Rosh. It’s a Gemara at the beginning of Nazir. It calls unnecessary fasting a Chotei. Fasting to fix a bad dream is not unnecessary. It’s the only way to fix that bad dream. And then, as a Middah K’negged Middah Kaparah, you need to fast again.