Sally, g'ah - sorry you got referred, though it's just what they do. I always trot this out, but 9 out of 10 referrals to breast clinics are benign, which let's face it are pretty good odds. 
The others have covered what will happen at the appointment, but in terms of taking someone or not, it might be worth trying and find out if your hospital does results on the same day or not. If you go to their website, that might tell you. My hospital did, so I had all of the tests in the morning, then went back at the end of the day for the results. If you can find out, it might help you to work out whether it's okay to go alone or not iyswim.
Hope you've got a very large glass of wine tonight. Be better once you know, and I still think you'll be fine. Stick with us for lots of hand holding, and ask as many question as you want. Really doesn't matter how daft or trivial. 
LGF, how sweet that he likes his bed.
Really hope the others don't catch it, and more's to the point, hope you don't either. What day of your cycle are you now? Can't remember where you're up to.
MAS, mediation lunch mention has made me hungry. Sounds like an excellent way of spending the day though.
SR, you've got a decorator coming in, with a kitten.
I predict alternative paint patterns. 
I've just had a very indulgent day. Went to see a friend's play at the matinee, which involved a long train trip there and back. Just me and a book - can't remember the last time I did that.
Am going to cook nice food for DH now to compensate for neglect. 