Does over treatment of hypertension i.e below normal level,cause any harm to kidneys or any other organs ?

Under perfusion: You want to take exactly the right amount of medicine for blood pressure control --not too much, not too little. You can monitor your blood pressures at home these days. If you took too much medicine and the level is below normal, be careful about falls. Drink some fluids and/or take in some salt - that will raise the BP back up. Best to call your doc for management. A brief time with low BP is OK