Yea - very likely caffeine withdrawal.
It should be subsiding in the next day or two.
You've read about P&B shakes. - Its a combination of products used for colon cleansing.
Its mentioned often on the bowel cleansing forum.
The fact that you have read it on this forum is because some people fall for this gimmick called "The Ultimate Cleanse". - Its The Master Cleanse
with P&B shakes added to it.
I believe its the name that really sucks people in.
If someone wanted to make sure that others don't experience the true benefits of the Master-Cleanse
then the "The Ultimate Cleanse" would be the answer.
Here's another persons take on the subject - //www.curezone.org/forums/m.asp?f=479&i=41