It shouldn't set you back to day 1 unless you did it more than once, but I am not expert an that matter. Of course your going to feel like crap, but relapsing is part of the progress and you'll learn from it and grow stronger. All you can really do is get back on the train and start again, but don't worry you are not the only person that relapses, everyone relapses at one point during there reboot. It's important that you don't get to upset with yourself it will only feed your addiction and make it stronger. Calm yourself my friend, everyone here knows what your going through and it is really tough, but you will get through this and your going to feel great afterwards, although I'm still in recovery myself. Try mediation, walking, reading, sports and go to public places and hopefully this will help. Best of luck.