I agree with everyone else. My daughter used to stand up from a chair and stretch her arms over her head--then PLOP! she'd faint and fall flat. It happened several times around 13-15 yrs.old. The doctor said to be sure to eat a decent breakfast--one that contains carbs and protein. After that, I made sure she at least ate SOMETHING for breakfast and it stopped. However, she still (at 30) will faint if she has fever. I believe it's all tied up with blood pressure and blood sugar. Please take care of yourself!
Soibhan