Why do i get lightheaded a lot had normal mri 4-18-13 & normal mra dec2012 no high blood pressure or any other health problems is this bad? & head pain

May be BP problem: You have symptoms that suggest a problem called autonomic insufficiency (dizzy spells, passing out, headaches). This is common in young women. Essentially the brain can misread the signals being sent by the heart and blood vessels and cause the pulse to go fast (or slow) and the blood pressure to fall making you lightheaded. A tilt table test can diagnose this problem. Talk to your md.