It’s my understanding that there’s two main categories of non-life threatening illnesses: מיחוש בעלמא, “average pain,” and נפל למשכב, one who is so sick that he’s unable to get out of bed. The former category is unable to take medication on Shabbos; the latter is, as well as certain other leniencies on Rabbinic prohibitions (see SA OC 328 for details).
Which category does someone with clinical depression fall into? People with clinical depression tend to constantly feel sad and have lack of interest and motivation to do anything. Does that qualify them as a נפל למשכב to be allowed to take an antidepressant on Shabbos, or are they still considered to have just a מיחוש בעלמא and it would be prohibited?
I’m specifically talking about someone diagnosed by a professional as having clinical depression, has been prescribed an antidepressant, and is not suicidal.
EDIT: It has been brought to my attention that it’s a dispute amongst the Poskim whether one who takes medicine regularly may continue to do so on Shabbos. It would therefore seem that my question only applies according to Rav Moshe, cited there from Igros Moshe OC 3:53, who holds that one may not continue a regular dosage on Shabbos.