Hello,
First 3 days can be hell, so I would advise to start on the weekend atleast so you don't have to go to work. I am on day 9 of my Water Fast and on my second night I had a screaming headache and vomited some bile. But hey even though it was hell the trick is to never give up just ride it out. It will pass. Do what you got to do - pray, meditate, stay in bed !! It will pass. Since my 8 hours of hell it has been smooth sailing. Infact everyday has got better and better, and right now I am feeling amazing !! It is worth it, if you really really want it.