What is it that you are "tempted to do..." this Monday? Just making sure that I am reading you right. If it's just finding energy and figuring out how you can get started on things, of course, as the old saying goes "the journey begins with one step," may not apply to you here. With the fasting & the juicing, etc. Just be sure that you are being careful to maintain an adequate amount of nutrients. And not too much sugar, or fructose (not sure what kind of "juicing," we're talking about?)...
But- if / or as long as you've got a sufficient supply of savings, in terms of that which to burn, then fasting can be very helpful & beneficial, as you're just going to be burning those calories you've got stored away (or "in storage,") . . . for energy~
It is, however, more concerning if this is not the case. And especially if you are 'under.' Unless being done for religious reasons, to clense organs, etc. So you may be tired and worn out just because of that. You're deprived of nutrition. Hopefully the doctor can run some tests and help you out further, or more conclusively ("You're lacking, or deficient in these areas...") / Good Luck!