Apprehension

I'm thinking now about doing a water fast, but I have many misgivings. I would hate to starve myself as my metabolism is being treated with levathyroxine (hypothyroidism), and it seems reckless to screw around with that. Maybe someone here could give me something to show my doctor, so I can do it with her supervision? I'm pretty sure she wouldn't know much about fasts or anything of that kind, so I'll need to give her some info.