Going today for Lupron injection how scared should I be?

I wrote this last week but can’t find my post. My father who was 91 has had Gleason 6 for 20 years within the last three months his psa has risen to 16. PET scan says cancer is still confined to the prostate. He tried the orgovox for one month every day but was continually sick with nausea. Dr is switching him over to Lupron one injection twice a year. How bad are the side effects? He wants to have quality of life. He is still active and healthy at 91 thank you.