I think I'd wait until after, and use EFT to keep calm during the water fast. Water only will not harm you, and will help the healing. How long are you fasting? Maybe Chris will come by and answer you, in a better way.
I just posted a Vit D post in the Natural Hygiene forum, that you might find interesting reading. It's from a site that allows you to research the world's healthiest foods also. Good site, I have found. I'm just now looking into best sources of supplemental D, since I've not taken isolated supplements for some time. I'm not a big fan of bottled and packaged anymore, but these are challenging times...low sun
and all.