Dress shopping: shouldn't I be excited?

I’m supposed to be dress shopping this weekend. My mum and my sister are coming from their respective homes and I’ve got the appointments booked.
The Boyf spotted it first though, the thing I was trying to avoid admitting to myself: I’m not really looking forward to it.
I’m nervous. No, strike that: petrified. And I can’t work out why. I LOVE to shop. I pride myself on being a good shopper, for myself and for other people. Sometimes I go out and try things on just for the hell of it.
So why on earth aren’t I prancing around in glee at the thought of try on lots of lovely wedding dresses?