It's quite easy to get into a not eating cycle when you are well fat adapted, but IMO you often end up then lowering your metabloic rate as your body slows down to compensate for the lack of food, nothing to back this up apart from my own observations from my own experiance.
FWIW I was fairly conviced I had some form of ME that developed after I had my gall bladder out a few years ago, but the dr I saw was bloody useless so I gave up on that
So I can understand how it feels to be just bloody exhausted for no reason.
You know all those pictures of Adam and Eve where they have belly button? Think about it..................... take as long as you need........................