I keep feeling realy dizzy lightheaded every time i stand. my vision blurs out to white. it lasts 10 to 40 secs. can you help me? low blood presure?

Sounds like: It sounds like "orthostatic hypotension". It's a phenomenon which occurs when a person stands and their blood pressure decreases. So much so that they don't send enough blood to the brain and can cause you to feel lightheaded or even pass out. Many things can cause this so you should see your doctor. But you can lessen this effect if you rise slowly and stand for 20-30's or before moving.

It may be: low blood pressure as you said - orthostatic hypotension- when your body can't cope fast enough with changing in position. Make sure you stay hydrated and make sure you keep track of how much you bleed, orthostatic hypotnesion ma also be a sign of losing blood too fast.