In my comments to a previous post, I made the assertion that Rav Moshe Feinstein is cited incorrectly by Rav Zilberstein. While it is true that both say that depression can endanger life - it seems that they do not agree as to how. The following seems to suggest that Rav Moshe labels pikuach nefesh as something which leads to suicide or clearly diminishes ones life while Rav Zilberstein seems to feel that any major psychological pressure itself decreases life.
Igros Moshe(O.H. 5:18): Shulchan Aruch (O.C. 306:9): “It is prohibited to ask a non‑Jew to travel outside of the techum on Shabbos to notify the relatives of the deceased to come and to eulogize him. However concerning a terminally ill person who asks that his relatives be notified it is definitely permitted.” The Levushei Serad says that it is permitted to pay a non‑Jew to travel so that the sick person won’t become severely agitated (tiruf daas) since this is included in the category of pikuach nefesh which permits violation of Shabbos. However I have not found any basis to permit this for the sake of a terminally ill person to prevent him from getting severely agitated (tiruf daas) – except for a rabbinic prohibition. I am astounded that the Levushei Serad said that it is permitted because of pikuach nefesh. His explanation that tiruf daas (severe agitation) is a sickness which endangers the person. That is only so for a healthy person who might come to commit suicide because of his agitation. However for a terminally ill person (shechiv m’rah) there is no basis to be concerned for this and therefore this is not considered pikuach nefesh. However more thought is needed as to what the actual halacha is in this case.