10-30 days sounds way too long if you haven't had experiences doing it before, it's especially risky at the moment when you break the fast and start eating again.
I'm interested in fasting as there are certain recent studies indicating that it can "reset" your immune system in a way (
link), however, 72 hours is apparently enough to trigger this effect. I had a go at fasting a couple of years ago. The first 24 hours were easy, after that I started getting palpitations, and by the 40th hour I felt so weak I could hardly work or do anything meaningful.
Regarding the meds, I would assume the absorption might get slightly higher if they are taken on a totally empty stomach like when fasting, but I can't really give a specific answer to this.