I, like you was very tentative and fearful about doing flushes, but once I got started, I wondered why I hadn't started much earlier!
I've done over 20 flushes and never have had a stone stuck. Hundreds, if not thousands have come out of me without any pain at all. I have only once had very dull and very bearable discomfort (in between flushes) and have used the tried and true method of using a tablespoon of epsom in a glass of water) and it was dislodged.
Do not let fear stop you from starting your healing journey.