Watcher - sincere condolences for the loss of your precious DD. I hope one day that you will find peace with the fact that gene carrier or not, you are not responsible. 
If possible, being a dependable sort, (as you are for we nocturnals here on MN), I would come and be your wingwoman tomorrow for dogs, ds and cat. I think all will be well without yours truly though, because it's just one day, and dogs, ds and cat will survive, or at least just about until you're back on duty to pick up the pieces later on!
I think this is one of those situations where you have to feel the fear and do it anyway. Easier said than done, but it's essential, so what choice do you have? If you put it off, you're just prolonging the agony for yourself and the family, and you'll have to go through all this pretest worry yet again. I think you'll feel better with it behind you than in front of you.
The worst has already happened to you with the loss of your precious DD, and you also mention issues with your ds, so I suspect you are no stranger to big girl pants. Hoik them up tomorrow, as high as you can manage, and get it over with.
Your mantra has to be: the test is essential and the test is safe.
Oh, and drink tea - keep off the fags. 