I like Suz's reaction: Gulp.
I'm still on the train too. I will offer a few things that may be helpful, as I have been musing over this for the last couple of weeks. First, it is the initial break that is the toughest. Once you get past that, it won't be so hard. So don't lose heart!
Second, I think it is helpful to replace the shopping experience with something else. A lot of us shop for emotional reasons (at least I do), so we can't simply stop. We need to have something to replace the shopping, so that our emotions still get the outlet they need. In my case, I was thinking about maybe spending more time doing my own nails or experimenting more with different looks with makeup (see Lisa Eldridge's videos online, for example). I already have an assortment of nail polishes and makeup, so that won't cost squat.
You could check out books from the library about fashion and read them instead of shopping. But I suppose this could go two ways: it could either let you get your fashion fix without spending a cent, or it could fuel your desire to shop further!
Can you go through your closet and consign anything? I just did that, and that took quite a bit of time. But it's still fashion related, and it will get you some money for your trip to boot.
One thing that I am starting to see is that the more stuff I buy, the less I get to wear what's already in my closet. I have some real favorites in my closet but haven't been wearing them as much as I would like because they get passed over in favor of the new stuff. If I want to spend more time wearing my favorites, then I need to stop adding to the stuff in my closet. Would thinking about your shopping in this light be helpful?
ETA: I wanted to say that in regard to the initial break being difficult, if you can find something to replace the shopping for maybe a month, you might find that you have successfully passed any "withdrawal" stage. Shopping, for many of us, is a habit, and if you can break the habit by substituting another one, you will find saying no much easier, I think.