The highest blood sugar level I have had in a medical test is 293 mg/dl (16.28 mmol/L). People don't come back from that level, but I did. It took me four weeks to research type 2 diabetes, and a further eight weeks to bring my blood sugar levels back into the normal range. That was more than five years ago, and for the most part, they have stayed there ever since. You probably noticed I used the words "for the most part", and that was deliberate...