I am so sorry i never answered you, and i guess you already had the operation now? I know how hard it can be to fast especielly when you havent done it for a while (or maybe fasting can be triggering as well). I dont know if you're allowed to drink or not, but if you're allowed to drink then tea is helpful and it might not still the hunger but it is atleast something in your stomach, or chewing gum (maybe not the best, if you are having an operation on your teeth).
I have had to fast many times while going to the hospital and i hate it, im not a huge breakfast person so that doesnt bother me, but when i have to fast all the way to lunch time then i find it tough and my energy drops and i get very thirsty as i amnt allowed to drink either. But its just "to do it" in a way, because there is a purpose to the fasting. However if you ever have to fast again and find it very tough mentally or physically then just talk to the doctor/nurse/dentist and see whether you can eat something smalll or consume liquids etc, they are all humans. During my recovery and when my body was used to eating at certain times, i found it tough when i then had to fast for different medical tests being done and one time when i had to fast from 8pm to 12pm the next day i just told the nurse that i didnt want to do that. I didnt feel comfortable fasting that long as well as i found it triggering (this was back in 2012/13), and then they compromised and i could eat my last meal by 8/9pm, and i would be allowed to eat after the first two tests instead of waiting until 12pm. However remember certain blood tests and x rays/CT scans require an empty stomach when done... just a note, if anyone is getting those things done.