Yes, the feelings you described (harder pounding of your heart, feeling nervous) are normal, you are obviously attracted to this girl and these reactions are normal... It is just good when you try to reduce your attachment to her if there is no chance that she feels the same, being heartbroken by someone who does not reciprocate your feelings is useless and painful.
If you have souvernirs, small things,gifts, photos etc which might remind you of that girl, bring back nice memories which might be painful now etc...,try to get rid of them or hide them somewhere where you will not see them. Do not listen to songs which might bring back those memories...
In my case it also helped if I did not meet or contact the person - at least for some time which is needed for emotional "recovery".
Today I happened to see the girl I was talking about and my heart started pounding harder and I got a bit nervous. Is this normal?
Yes, I followed the advise by Severin and it worked but the act wasn't that pleasurable.But yes, it worked.
Read your own letter out loud as if it were addressed to her from someone who was almost a stranger and I think you will have your answer. You are not in any type of affair, lust or otherwise. What you have now is basically the same as you opened up an adult magazine and wanked off to that.
You stated that you idolized her, and admired her both physically and emotionally. That my friend is only one corner of the triangle (pathos) and you ignored logos and ethos probably creeping her the heck out. You need to get more experience just dealing with people so that you can realize that women are different beasties than men but they are not gods either (though I know all too many who think they are goddesses) .
You need to meet and relate and realize that even if each person can have sex, just because they have sex with you doesn't make them special, nor, honestly does it make you special.
Be Blessed
I would recommend you to try some of these things:
-if you masturbate and you start to think about her, OK, but as soon as you are going to reach an orgasm, try to think of someone else, some other girl(s), fantasy, picture, video etc... So, if it is not possible to stop thinking about her during masturbation, try NOT to think about her during your orgasm. If you are about to have an orgasm, then you will possibly be able to have orgasm also with another image in your mind, maybe the pleasure will be weaker, but it will be an orgasm and it may help to re-programme your mind which seems to be attached to her so much.
-try to masturbate using visual images of other girls, I do not want to lead you into so-called "porn addiction" or "porn obsession", but in this case some visual stimulation may have therapeutic effects. You can try to use any pictures, erotic pictures, dirty pictures, porn, or even "polite" pictures in magazines - even masturbating to the portrait of Britney Spears may be better than getting stuck to the images of the girl when this obsession troubles you. (And I agree with you that it is a good starting point to break the connection between your masturbation and thinking about the girl you mention, you need to move on and not to ruin your emotional life by being heartbroken forever)
-in non-sexual situations, try to find out some negative points related to this girl - however small and petty details - and focus yourself on these negatives of the girl, however silly it may seem, it can be her accent, her nose, her political views, her parents or friends - whatever which may help you to stop seeing her as an "angel", "perfect and flawless being" etc
-try to spend a lot of time with other people, good friends, or nice and attractive girls, if you can get surrounded by other attractive and nice girls, enjoy their company, it should help you to re-programme or re-condition your brain too
Don´t worry, the emotional pain you experience now is normal, it happens to us, and we have the power to overcome it, sooner or later you will be all right, maybe there are other traps waiting for you, other girls who will hurt you, but do not give up, we can learn also from painful experience and you will grow stronger by it - and strength is really something which we need to survive in this world.
GOOD LUCK and TAKE CARE