What Causes Blackouts, Vision Whiteness With Residual Dizziness And Headaches?

Hi,For a year or so I have been having these blackouts except instead of fainting every time ,my vision goes completely white, and all i can do is hear and move slowly to hold on to something or sit down because if I don't I faint for real. They are really dizzying, disorientating and give me short head aches after. These can happen at anytime of the day, anywhere.