I've been there. Just don't make a habit of it, like I did. Making yourself sick, by the way, for something like eating too much chocolate, does sound like a bulimic action. And it's addictive. I lost two stone over the space of two weeks because I'd lust do it every time I ate- and this was with no history of anything- I didn't consider myself to be bulimic because it was such a new thing. Then I passed out at work.
As for why your chest hurts, the same happened to me for a bit as well. Mostly it was when I couldn't successfully vomit, so it could be the fact that your oesophagus became stretched with the amount of food that got stuck if you couldn't bring it up.
Honestly, do yourself a favour and don't do it again.