The way the doctors in the ER or your physician will determine blood loss is by asking you how long do you go in between changing a saturated pad or tampon. The rule of thumb on this is if you are soaking through a pad or tampon every one to two hours this is of concern. Anything beyond that is considered within the norm but heavy bleeding. Clots are normal. You may be anemic which would cause you to feel light headed, nauseous and pass out. Call your doctor or go to a clinic or ER if you are passing out. This needs to be looked in to. Hope this helps.