im an alcoholic too, but i know quite a few people who have gone through heroin withdrawal....sat by one for support once too.
i know right now you feel terrible, i think you are probably at the hardest point. the good thing is you are safe, generally speaking. alcohol withdrawal can kill you, heroin withdrawal just feels like it will.
every person ive talked to said epsom salt baths worked great for the body aches and pains. the anxiety is a tough one, but at least you recognize that you are in fact safe. also keep telling yourself that it will get better, because no matter how you slice it, it will if you stay clean. just keep at it, don't pick up and it will get better.
also, i think coming clean with your sponser is a great idea. i know it is a hard thing to do, your brain will give you all sorts of reasons not to. but your sponser is there to help. there is no judgement, many people have relapsed before you and many people will after you. try not to feel shame, its not worth it. once you tell someone, then you will have in person support as well....and personally for me that makes a big difference.
remember you don't ever have to do this again.