I have heard about a Biblical prohibition on causing oneself to suffer during Yom Tov. The example that always comes up for this mitzvah is the permission not to sleep in the sukkah if it causes one to suffer.
First of all, I don't understand how the sukkah example is not a violation of the usual principle of prioritizing positive mitzvot over negative ones when there is a conflict. (Both, I think, are Biblical mitzvot.)
But in general, to what other situations/issues could/does this mitzvah apply? What are the limits of its application, especially in light of competing mitzvot? (i.e. could it discharge one from positive mitzvot but not negative ones? From Rabbinical but not other Biblical ones? ...etc.)
For a bonus, please bring examples of piskei halacha in which this mitzvah has been used to justify loosening the usual strictures of Yom Tov for suffering individuals (or for everyone). One example already is the shower issue.
Related (Please don't judge): How to have an easier time with Yom Tov?
CYLOR if this applies to you (I have and I will)