On a particular day my pp blood sugar value was less than fasting sugar value. how is this possible.?

Insulin surge: Pay attention to the foods you eat. You will discover that your body handles some foods extremely well, & others are triggers for high blood sugars. For example, it is possible that because peanut butter has a few carbs, more protein, & even more fat grams; an Insulin surge is created thus lowering your blood sugar. You wouldn't expect this, but use foods for their nutritional/metabolic effects!