Why fasting sugar sometimes more than post lunch sugar?

Blood sugar level is a result of two controlling factors
1. Sugar Intake
2. Insulin response by the pancreas after meal. The pancreas creates insulin which brings down the blood sugar level. A heavy meal will cause increased secretion of insulin in a normal healthy adult. So surprisingly the heavier the meal (sweet Food) you consume lower will be blood sugar level. In patients, on treatment who takes tablets / Insulin before meal the same effects are seen.
During treatment of diabetes fasting sugar is maintained at higher level then post lunch sugar to prevent complication of hypoglycemia during sleep.