Today i ran a mile and i felt fine for about 3 hours, but now i have a headache, i'm dizzy and i feel like throwing up. i'm not dehydrated, i drink water all day, so why do i feel like this?

Sounds like low BP: Those symptoms are often associated with a low blood pressure. It's easy to check...Take your BP sitting and standing. If the BP decreases to below a systolic (upper number) of approximately 90 with standing, it's consistent with postural hypotension (low BP upon standing). Usually, it will correct with drinking more fluids. Gatorade has salt in it and will raise the bp.