Extended fast.. is it safe?

I'm interested in an extended Water Fast (21-28 days). My reason for fasting is illness, I have suffered with diabetes since I was 15 (now 23) that can't be controlled by medication & I struggle to control with diet. My bsl is always 450 mmol/L +.
I also have PCOS, liver & kidney function abnormalities, hypertension & an abnormally high heart rate. I've also recently started experiencing severe pain in the lower half of my body that makes it near impossible to sleep or focus on everyday activities.
I have done several shorter Water Fasts (3-7 days) but am wondering if a longer fast would be safe as I'm not overweight? I'm 5'3 & 113 pounds.
Any advice is greatly appreciated :) Tweet