Yom Kippur is called “Shabbat Shabbaton” – it is doubly Shabbat and so its sanctity. Like Shabbat, labor is forbidden on Yom Kippur but, unlike Shabbat, so is Oneg – bodily pleasures. Its total dedication to God is sometimes thought to justify fasting even where it might somehow cause – not just temporary and minor physical discomfort – but more serious medical problems.
However the mitzvah of “afflicting one’s soul” does not undermine the principle that Shabbat and Yom Kippur and all of Jewish law, for that matter, are not intended by God to cause physical or emotional damage.
The Talmud makes the point with a beautiful metaphor:
The Talmud ruled that if either a sick person or a doctor felt that life was endangered, the Shabbat must be suspended. The opinion of two doctors who felt danger existed took precedence in Jewish law over the opinions of 100 doctors who felt otherwise (Shulchan Aruch O.H. 618:4).
Similarly the Talmud ruled that even if 100 doctors believed there was no danger, if the sick person maintained that s/he felt endangered, then the Shabbat must be suspended – “for the heart knows its own trouble” (Proverbs 14:10) (T.B. Yoma 83a).
The Jerusalem Talmud was even more emphatic: “[In life-threatening situations when the Shabbat must be violated] the one who acts quickly is praiseworthy, the Rabbi who is asked his opinion deserves blame, and the one who asks the Rabbi is a spiller of blood.”
Maimonides continues to expand on the ultimate value of saving human life even on the holiest of days.
“In fact, whatever must be done to avoid a suspected life-threatening danger is to be done not by non-Jews, by children…but by the greatest scholars of Israel. One may not delay desecrating Shabbat for a dangerously ill patient, for it says “do whatever a human being needs to in order to live – v’chai bahem” (Leviticus 18:5) – and not die (Sifra). That teaches us that the whole purpose of the laws of the Torah is not to bring vengeance into the world, but rather to engender compassion, kindness and peace in the world.” (Maimonides, Mishne Torah Shabbat 2:3).
And Maimonides continues: And those sectarians [the Karaites] who say that this is a desecration of Shabbat and forbidden – of them it is written “Also I have given them statutes which are not good, and laws they cannot live by.” (Ezekiel 20:25).
There is no justification to understand fasting on Yom Kippur or refraining from work on Shabbat as an expression of a Judaism or a God who loves suffering and sacrifice for their own sake.
Rabi Yisrael Salanter once preached: “It is usual for a people to express concern for their own body and for their neighbor’s soul. They seldom worry about their own soul and the other’s body. However on Yom Kippur at least, we should disregard the needs of our body and pay attention to our soul. We need not concern ourselves with our neighbors’ souls but chiefly with their bodily needs.