I agree with you. Sounds like you are speaking from experience, mine is the same. Fasting is kinda like hibernation or seeping, parts of your system shut down and repairs take place, and you are not meant to rush around, you just want to rest, you are running on batteries.
On my brief juice fast trial, I found my energy levels were high. Juice fasting is not really fasting, its like feasting, with a mechanical stomach outside of you (a blender or juicer) doing all the work your digestive system would normally do.