I, too find I am wildly enthusiastic, energetic...

and eager to do stuff, then shortly find I am nto really that full of energy. And I oftn poop out after a long walk/hike over the SF hills. I sometimes am even fatigued the next day. My understanding of the Master-Cleanse is that the energy supplied is enough for normal daily activities, not for athletic pursuits... this is about healing and the body does it's healing when we rest.
Take it easy for the next few days, have plenty of lemonades and rest alot.. see how you feel. Cravings and fatigue can also be a major sign of deep detox. You may have loosened up some old stuff.. and it wants out. Let it go!!
Your body will tell you absolutely if it needs nutrition - and you are allowed to stop any time you wish, as well.
Best,
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