What you choose to say to your doctor is up to you. But please understand that when you have symptoms of an illness, the illness itself does not know that there is a holiday and that you cannot be sick. Your doctor is no more than human-- he can try to help but no one can guarantee that you will not need medication or be free of these symptoms on Yom Kippur. As Susan suggested, continue to work with your doctor but you cannot make requests to be cured by certain dates, it is not humanly possible to say "You will be cured by Yom Kippur." Certainly you can mention your upcoming religious holiday to your doctor, but please don't expect him to give you a guarantee that you will be cured by that date.