I Am 21 Years Old. When I Stand Up, Especially

I am 21 years old. When I stand up, especially when I stand up quickly, I get very lightheaded and dizzy, and I get a pounding headache. I have talked to my family doctor about it and he ordered a tilt table. I get the results the 5th of January, but the nurse didn't react like anything was going on.. I'm not too sure tho. I just wish it would stop. I would greatly appreciate some feedback.