Will my blood sugar be too low after fasting? it is 4.8 after eating a lot of sugar, (my colleague was 6.4 after eating the same). if i fast 12 hours will it be too low?

No, your: Body is smarter than you are. Fasting doesn't drop blood sugar below normal because your body is very protective and keeps dumping glucose into your blood stream to maintain a normal glucose. Otherwise you wouldn't be able to survive sleeping at night, would you? There is no hypoglycemia unless on diabetes drugs.

Need more info: Are you a diabetic on medication? It you do not have diabetes, your blood sugar is regulated by a number of hormone systems to keep it in the normal range regardless of whether you are fasting or eating. People who starve do not die of hypoglycemia. If you are medication for diabetes that causes release of insulin, then you have the potential for low sugars to occur.