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.
Shabbat is suspended when it comes to danger to human life…even if there is only a suspicion of a life-threatening condition. When a pregnant woman is giving birth that is by definition a life-threatening emergency, so one descerates Shabbat by calling a midwife from another location, cutting the umbilical cord and tying it.
In fact when a woman cries out during labor that she needs a candle, even if she is blind, we light one for her. For this will cause her to (relax emotionally and) maintain her sanity – even if she cannot see. …” (Maimonides, Mishne Torah Shabbat 2:1,11).
The Talmud makes the point with a beautiful metaphor:
Someone asked Rabbi Tanhum: ‘What is the ruling regarding extinguishing a candle on Shabbbat for the sake of someone who is ill?’ Rabbi Tanhum replied: Both a candle and the soul of a human being are called “a candle / ner” (“For the soul of human is the candle of God.” – Proverbs 20:27). Therefore, it is better to put out a candle lit by flesh and blood rather than a candle lit by the Holy One.” (TB Shabbat 30a)
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.
Rabbi 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.