Every cleanse is different. I did a very long fast a couple summer ago (60 days) and never had a moment of trouble until day 18!!! The longer you fast the deeper you cleanse. They say you cleanse starting with the most recent crud and work backwards... seems true from my experience.
The day 18 crisis lasted about a week (kidneys), then smooth sailing to day 57, when a packet of DAY GLO ORANGE BILE exploded in my colon!!!
YIKES! Suddenly it's like the worst flu of your life... for about 24 hours. Then just as suddenly you feel fabulous.
This is why it is critical to keep your colon clean, every day you fast!