Hey i am 13 years old.. And i need to know if i have low blood pressure. Whenever i sit or lye down then get up i have a blackout/dizziness/ & a really bad headache this happens most of the time when its hot out or when i run a mile at school.. this has been going on for about 2 years.. after the blackout i have a really bad headache for several minutes.. One time i ran a mile at school and this happened to me i went to the nurse they sent me home and my mom took me to the doctors.. they didnt even mention low blood pressure. even tho i am having low blood pressure symptoms..if i do have it what causes it and should i go back to the doctors?? thanks to anyone that replies back! :)