From your symptoms it appears that you are suffering from Orthostatic Hypotension – otherwise known as a “head rush.” Orthostatic hypotension occurs when a person rises to a standing position from a lying or sitting position and is a result of falling blood pressure of 20 mm Hg systolic or 10 mm Hg diastolic with or without an increase in pulse rate. The symptoms typically include dizziness, light-headedness, temporary blindness, body dissociation, extremity tingling, or even fainting. These symptoms are a result of insufficient blood flow to the brain.
The most common causes of orthostatic hypotension can be divided into 3 catagories: Volume Depletion, Neurologic Abnormalities, and Medication.
Volume Depletion either from dehydration, anemia, or excessive fluid loss (diarrhea, vomiting, anorexia) can result in decreased intravascular volume and low blood pressure that can further be exacerbated by standing too fast.
Neurologic disorders can result in the inability of the body to constrict blood vessels in the leg as a person stands resulting in too much blood pooling in the legs and the symptoms of orthostatic hypotension. Typically, this occurs in people with nerve damage, diabetes, dysautonomia, or other genetic/neurologic diseases.
Lastly, medications such as diuretics, antidepressants, or nerve blocking agents can cause orthostatic hypotension as part of their side effects.
It is not uncommon for people your age to suffer from orthostatic hypotension especially if you are in a growth spurt. However, you should be evaluated by your primary doctor to see if there are any medical conditions contributing to your orthostatic hypotension.