Hi Yen,
My friend told me, her husband saw so much blood, so ask the nurse to change for his wife. then the nurse not very happy, and say she just changed, and can not change so often. so, the husband went back. but then, he saw the whole bed with blood, so went to call the nurse again. and the nurse only came after 15mins.
but when they saw so much blood, they called in 5-6 nurses & doctor, and put my friend into ITU straight away.
Although I haven't see it in personal, but from what my friend said, I guess you should be able to tell the difference between normal bleeding & serious one.