Lightheaded and then Heart "Pain" and Slight Difficulty Breathing?

Hi, I'm a girl and I'm 15, and for the last year or so I have gotten very lightheaded occasionally when standing up. Sometimes it is worse than other times, but it doesn't happen every time I stand, although twice I blacked out and actually fainted (or at least that's what I presume, as I don't actually remember falling), the second time hitting my head on my mom's metal exercise bike. It kind of worried me, but I wasn't sure if it was serious or not. I don't get lightheaded all that often, and it never lingers for more than 30 seconds, and when I told my dad he told me it probably wasn't too serious, but to tell him if it ever happened again (which, thankfully, it hasn't- so I haven't actually seen a doctor about this).

I did a lot of research online and I found that blood rushing to the head was quite common upon standing, but I didn't see my other "symptoms" in my search. Those "symptoms" only happen in the worse spells, and those are that I lose my balance and have to lean against a wall or such (and wait for the blood to rush back to my head), with my vision being a sort of black, while I feel a peculiar pressure in my chest, almost as if my heart is "restarting" (for lack of a better term), and beating so hard, that I feel it without searching for a pulse (palpitations?). I'm not sure if it's painful or not, but it is definitely not pleasant. I also sometimes feel that I can't get my breath during those spells, or that my breath is caught, and as a result of the breathing and the heart-pounding and lightheadedness, I sometimes feel very, very close to passing out again.

It has slightly escalated within the last year, but since it still only happens occasionally (the bad spells being maybe 2-5 times a week, give or take) , I fear that if I do ever feel it is necessary to go to the doctor, nothing will be wrong with me and that they'll tell me I'm being an over-dramatic teenager and then get on with their next patient (I haven't exactly had good experiences with doctors, especially not those over-worked walk-in doctors).

Anyways, do you guys think it's serious, or am I just being over-dramatic? I would like your guys' opinion. Do you think this might be anemia? I looked up the symptoms, but the dizziness and light-headed-ness are the only symptoms that seem to match. I don't know... Anyways, I would appreciate any feedback!

Oh, and here's a little background health about me. I'm in shape, and on the track team, although I probably should eat a little more healthy. I don't have any previous medical problems other than a fractured wrist and a stress fracture on my ankle. I'm generally pretty healthy, however, and this is the only long-lasting strange medical problem(?) I've ever had.

Thank you!

(Not sure if this is specifically Cardio related, but I wasn't sure where else to post it).