I can relate to this SO much
I was in my mid-twenties before I learned how to stop talking. I tend to fill the vacuum of quiet which naturally occurs when people are thinking or done talking. That quiet still makes me itch all over. I feel pressure inside to quickly fill it up, but that's impossible and ill-advised.
It took me much longer to learn the importance and even the power of silence.
As far as diagnoses themselves, I've been relieved to get a diagnosis before, but really, the relief came well before an official person gave me the official call. In the case of the D.I.D. (multiple personalities) the official diagnosis was probably more... relevant to me because it was such a hard to believe issue.
The depression, the bipolar issues, especially the bipolar diagnosis at 19 was a relief to me because it just explained SO MUCH.
I can also see the side of things of not needing external diagnosis as well.