From: Rabbi Moshe Sofer
To: Rabbi Naftali
The Chasam Sofer refutes three arguments raised by Rabbi Naftali regarding how to arrange a valid get for the wife of a man who alternates between lucidity and insanity, distinguishing the case from the Noda BiYehudah's ruling on the wife of an apostate and from rabbinic-level vestos concerns. He nonetheless upholds his earlier ruling permitting the wife to appoint a shliach kabbalah on independent grounds, and adds that if the husband's insanity has identifiable external causes requiring medical treatment, he is fully competent during lucid periods and both forms of agency may be used without restriction.
Source: Shu"t Chasam Sofer EH II §44