High blood sugars during fasting can happen if the subject had a high blood sugar to start with or if some medicines are reduced or discontinued. If sugars are beyond 300 mg/dl, there is a risk of diabetic ketoacidosis. Further you can experience increased urination, excessive tiredness, fatigue and infections if sugars increase beyond 300 mg/dl.
Low blood sugar values below 70 mg/dl can result in dizziness, drowsiness, hunger, perspiration and convulsions. If your sugars are found to be below 70 mg/dl or above 300 mg/dl, it is preferable to break the fast and contact your health care provider. If the blood sugars are below 70 mg/dl, consume 150 ml of fruit juice or 2 glucose tablets and top it up with a snack.