Seems like a game right now. One day in the near future you will remember this and say. WTF happened....
If you get more, it could be the point of no return. I'd stop for a week at least.
Heroin is absolutely no more likely to get you addicted than any other (strong) opiate if you're railing it. IV however is another story entirely. I'd go as far as to say that railed h and shot h are essentially completely different drugs.