I fast all day on the day of a flush, and I think this helps a lot. The most problematic thing for me would be insomnia.
Preparation has a lot to do with it, and I think parasite and bowel cleansing ahead of time would be in order.
OTOH, you just may have blockages that produce pain when the gall bladder contracts. You should not have that blockage stuck like that if you do the preparation phase correctly. Lots of malic acid does the trick ...