That's great! I hope everything goes well for you! I got my diagnosis almost exactly a year ago, and it was a HUGE relief to me.
Try not to be too scared. I don't know what testing you will be doing, but when I went, I was SOO nervous! I was a wreck. I was shaking and near crying by the time I got to the psychologist's office. I'd never met her before, I'd never been to any kind of therapy, I had no idea what to expect. But then she was really nice, and she explained exactly what I could expect during the session. Then we talked about nothing in particular for a few minutes (she must have seen how scared I was), and I found myself confessing how scared I was that she wasn't going to believe me, and how hard it is to communicate to someone and get them to understand, and she said, "Well, there are still some questions I want to ask you, but you shouldn't feel worried about needing to prove anything to me. You may or may not be autistic, but I want you to know that I can already see some characteristic traits in you." We were less than 15 minutes into the two-hour session. When I heard that, I just cried and cried from the relief. And then I was much more relaxed and we could go on with the session.
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You don't need to hide, my friend, for I am just like you.