Well, I run the 30 Hour Famine yearly, and with about 80-150 participants, we usually have 1-4 faints during the famine, different people. I'd imagine that the number would go up a lot if it was a week. A LOT. It IS a possibility.
May I ask why you're doing it? Charity/weight/religious? What are your 'rules on liquids going to be (Just water, just transparents, anything at all)?
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I've done the damage, the damage is done.
I pray to God that I'm the damaged one.