Why if i accidently bump myself does it goes so blue over such a large area? sometimes i dont even noticed i've hurt myself until i see huge blue mark

How big?: Generally bruises larger than one's hand are considered abnormal unless there is major trauma. If they are smaller than that, it may be normal. Medications that interfere with blood clotting, like aspirin, anti-inflammatory pain meds and warfarin (coumarin) can contribute to bruising. If there is a sudden increase in the amount of bruising, then a medical exam and blood tests are warranted.

Bruisability: Easy bruisability May be due to capillary fragility, low platel ets, other blood disorders or coagulopathy,taking aspirin or NSAIDS like Aleve, (naproxen)corticosteroids like prednisone. A hematologist is best qualified to evaluate and advise you.This would be especially important if you're having blood from nose or gums,etc.