brother when going from synthetic to mineral you dont need to flush as all the sludge cleaning is done by the synthetic oil.
u are going the other way around
u have to flush as i am sure there will be sludge present in your engine as base oils dont do the cleaning as
synthetic oils do.
if you dont want to its your choice but before doing it
also ask some 2 or 3 mechanics or oil shop owners u will get your answer.