From the first moment when you are told that your child has something wrong your world is rocked. You become quickly accustomed to the fact that you will now face a whole new world of realities. You can throw away the books. You can ignore people's advice. You can stop asking your friends if their child did the odd thing you child has taken to doing. Reality is something new and different.
First you let go of the idea that your new child will be "perfect". I think every parent has the realization at some point that their child isn't perfect (and that no child is). They just probably don't do it sitting in a doctors office. Then you have to mourn the loss of what you envisioned. This takes time. And just because you mourn it once doesn't mean you are done. Oh no! This mourning will come in waves. You will think you have it all figured out and you can handle it. Then the next giant waves crashes and you start over again.
Then you will, on a daily basis, have to become adaptable and flexible. Each day will bring it's own new version of "reality". If you don't learn to adapt quickly you will fall on your face.
So on the day that you finally wake up and realize that what you thought would be "reality" is gone then you can learn to stand on your own two feet and face the new reality. At least until the next wave comes...