It is frightening to see a plant dramatically drop its leaves. I’ve had that happen with new plants when I forgot to water. If you look closely, you should be able to see tiny leaf buds that have formed for next year. Once spring comes, it will be interesting to see how high up it leafs out. By mid-spring, you will know if you need to prune back some of the branches. After the first year, plants usually have enough healthy roots to get them through changes in conditions with just wilted leaves rather than shedding all of them and scaring the daylights out of us.
Thanks for writing!