Well...I think it's all really hard to pin down. Dusan (starter of curezone) says that it's not imperative to have diarrea before the OO (Olive-Oil) drink. Oleg below doesn't even take ES...and I know lots of others who don't take the ES either (Stonehedge, Blueduck) and don't get sick and have great flushes.
I've never had diarrea before bed and I've only thrown up once out of 4 times...but, there was nothing I could put my finger on re: why did I throw up? I think it's planetary! ha.
Every flush seems to be different.
I DO believe that what is most important of all is to be FULLY hydrated before flushing...and the day after, too. Also...one must have diarrea somehow (by taking either ES or prune juice or salt water flush) the morning after the flush because we don't want those stones in there leaking their toxins into our blood stream. Ick!