Listening to Doctors

A sick person has an obligation to follow the advice of his doctor. If the doctor is advising something because of possible life endangerment and if you disregard you may be transgressing the issur of suicide. You old be considered a Chassid Shoteh , it is foolish and false piety.
There is not direct Gemara about this issue but the Poskim Rishonim and Acharonim deal with questions like this.
The Hagahot Ashri quotes the Maharich who questions whether if one wants to stringent and let himself be killed in situation where he is not obligated to give his life (not Avoda Zara Giluy Arayos or Shfichut Damim) if it allowed.
Tosfot Avoda Zara 27b and the Rosh say if a person let’s himself be killed for lesser Aveirot it is not called hurting oneself.
The Rambam Yesodei Hatorah 5:4 argues that anyone which it says transgress the mitzvah and don’t’ be killed and doesn’t transgress the aveirah and lets himself be killed is held culpable for his own death. The Ramban in Sefer Torat HaAdam adds that this is under the transgression of “Ach Et Dimchem Lenafshoteichem Edrosh”, the passuk which forbids suicide.
The Radbaz similarly says that such a person transgresses the issur of suicide and Al Tehi Tzaddik Harbeh (Don’t be such big Tzaddik as it says by Shaul and Amalek) and a Chassid Shoteh and Hashem will punish them for it.
The Chatam Sofer in the midst of a question about whether one whose brothers died from MIlah whether he can be stringent and do MIlah discusses this issue. He says the Rishonim who hold like the Tosfot would agree that he would be permitted to do Brit MIlah and he would be considered Kadosh if he risked his life for it. Both R’ Tzvi Peach Frank and Dayyan Yitzchak Weiss (Minchat Yitzchak 2:49) explains it would come out from the Chatam Sofer that our question about endangering yourself by going to Minyan would be dependent on the Machloket between the Tosfot, Rosh, Maharich against the Rambam and Ramban. The Rambam would not agree that one may risk his life and perform Brit Milah even if his brother’s died from the Brit MIlah.
The Ktav Sofer questions his father what about the passuk of V’Chai BaHem. The passuk in Vayikra 18:5 says :And you should guard my rules and laws …And You shall live by them, I am Hashem. The Gemara in Yoma 85a relates: It once happened that Rabbi Yishmael, and Rabbi Akiva, and Rabbi Elazar ben Azarya were walking on the road, and Levi HaSadar and Rabbi Yishmael, son of Rabbi Elazar ben Azarya, were walking respectfully behind them, since they were younger and did not walk alongside their teachers. This question was asked before them: From where is it derived that saving a life overrides Shabbat?
Rabbi Yishmael answered and said that it is stated: “If a thief be found breaking in and be struck so that he dies, there shall be no blood-guiltiness for him” (Exodus 22:1). Now, if this is true for the thief, where there is uncertainty whether he comes to take money or to take lives, and it is known that bloodshed renders the land impure, since it is stated about a murderer: “And you shall not defile the land” (Numbers 35:34), and it causes the Divine Presence to depart from the Jewish people, as the verse continues: “In the midst of which I dwell, for I the Lord dwell in the midst of the children of Israel” (Numbers 35:34), and even so the home owner is permitted to save himself at the cost of the thief’s life, then a fortiori saving a life overrides Shabbat.
Rabbi Akiva answered and said that it is stated: “And if a man comes purposefully upon his neighbor to slay him with guile, you shall take him from My altar, that he may die” (Exodus 21:14). The phrase “take him from My altar” implies that if the murderer is a priest and comes to perform the service, one does not wait for him to do so but takes him to his execution immediately. But one should not take him from on top of My altar. If he already began the service and is in the midst of it, one does not take him down from the altar immediately but instead allows him to finish his service…. Rav Yehuda said that Shmuel said: If I would have been there among those Sages who debated this question, I would have said that my proof is preferable to theirs, as it states: “You shall keep My statutes and My ordinances, which a person shall do and live by them” (Leviticus 18:5), and not that he should die by them. In all circumstances, one must take care not to die as a result of fulfilling the mitzvot.
Meaning anytime the is a conflict between a mitzvah and one’s life his life wins and there is no mitzvah anymore.
Another issue is that the Gr”a in Yoreh Deah 156:3 explain the Machloket between the Tosfot and the Rambam is only when a Goy commands the Jew to transgress a specific law, and then the Tosfot ss he can give up his life and the Rambam agues. Ro example if a Goy threatens a Jew to do Chilul Shabbat the Rambam would say tis forbidden to give up one’s life and Tosfot would permit it. This would have no application to risking one’s health to do a mitzvah because there is no one specifically threatening him.
LaHalacha the Shulchan Aruch in Yoreh Deah 157:1 rules like the Rambam and it is only permitted to give one’s life for lesser Averiot if it is a decree for the whole nation to not keep mitzvot like during Chanukah, otherwise V’Chai Bahem overrides the mitzvah. Also it is unclear whether one may apply the opinion of Tosfot to risking’s one’s life to perform a mitzvah so one must listen to their doctor in this case.