As far as the fasting discussion goes, I heard a story once and I don’t remember which gadol it happened with. A middle aged man was sick and the doctor had said it was dangerous for him to fast on Yom Kippur. This man however felt very strongly that he had fasted his whole life on Yom Kippur and wasn’t going to stop now. His concerned family turned to a gadol with the shaalah. The gadol immediately went to speak to the man who was adamant in his intentions to fast, despite the psak halacha to the contrary. The gadol responded that if that was the case he would forbid any shul from giving this man an aliyah again, as we do not give an aliya to an apikores! The man was astonished and the gadol explained that one who fasts when the halacha says he should not is not worshiping Hashem but rather he is “worshiping” Yom Kippur!!!
Every case is different, but if your posek has forbidden you to fast, then that is your avodas Hashem for the day!