It is said that harm may arise from a fast only if you are fearful of going through with it. Fear is a definite contraindication. So don't be nervous, and place yourself in the hands of Mother Nature where she serves you best. Fasting is her own method of healing so be confident. The attitude of mind plays a very important role.
Rest much of the time and drink pure water according to thirst. A blood pressure monitor would be useful if not essential, and take a reading first thing on arising on a daily basis. The main thing to watch for is any SUDDEN change in your vital signs such as a BIG drop in blood pressure, where it would be advisable to break the fast, but this is rare.
Keep us posted, you will have much support here if you ask for it. Any questions? Just fire away.