I have been getting very lightheaded whenever I stand up. It used to just be when I stood up fast or sat down for to long, but now it s very often. It was normal until one day at school I felt very sick, and got up to go to class, but I got lightheaded and dizzy, I kept walking until I lost vision and hearing and fainted. I went to the hospital and they took my blood but found nothing wrong with me. Why is this happening?
Hi there, it sounds like you might be affected with orthostatic hypotension, since you have been getting lightheaded associated with position changes. It can often happen in young people with low blood pressure at baseline, especially if you are a little tired or deny Chat Doctor.  I would recommend you make an appointment with your primary care doctor about this problem, as sometimes he or she can prescribe you a medication (like mid