You poor love, what a mess!
Your mother sounds incredibly awful - she must know you have these MH problems but she has pushed you to near-breakdown just to get her own way? Is she somehow "competing" with friends and/or family to have the best daughter's wedding or something?
I think at this stage you should probably find a way to go through with the ceremony at least, make it worth the guests' attendance; if you can get through that, then at least you WILL be married so that will be something good that came out of it.
After that - you do what you need to do. If that involves going home, or hiding out in the hotel room (if you have one), then do that.
If you can manage the wedding meal, great. If not, fuckit, let it go - if your mother has an issue with it then just remind her that this is HER "wedding", not the one you wanted, and she can bloody well play the grande dame if she needs a centrepiece.
You need to keep her away from you entirely before it, as well. Do you have friends/siblings who could do that for you?
I know I'm being pushy but I do agree that it would be a bit harsh on all the invited guests to cancel it at this stage, many of them would lose money on bookings/ travel arrangements. Talk to your fiancé and see what plan you can come up with - and stay away from your mother.