Why do I only feel 'normal' after drinking coca cola?

the simple answer to this is, you are addicted to the caffeine in coke. My daughter has been through this and the only way to stop it is to slowly wean yourself off it, you will get headaches etc but you have to persevere and just put up with the unpleasant side effects, but you will feel so much better once you are off coke and you have to stay off it for good. Good luck.