A short while before I was diagnosed it became suddenly so apparent that my previous diagnosis of Aspergers was so patchy and wrong, the more I learned about PTSD, the more I could understand why I did things, why I was affected by things, what was really happening when I'm triggered, how much of the time I'm triggered (that one's still very much growing in awareness), what flashbacks were and why they haunted me so frequently, why I didn't trust myself or others and why I self-sabotaged to name a few. Also with the understanding of what dissociation was and how I had barely lived a day without filling it with some form of dissociation for over a decade and nearer two, has also provided me with great insight.
That doesn't mean I'm relieved to have the diagnosis' affects, just that I can recognise them as what they are and as such either chose to stop there or investigate them further and perhaps tackle some of the underlying problems. I agree that it was validating, for me it meant that I didn't loosely fall under the diagnosis of Aspergers and my behaviour was out of my control - which felt like a lie even to me, it meant that even though I can't control all of my behaviour now, I might, in time, be able to control some of it in the future. It also means I can finally see that I need some personal recovery for the first time.
Good post! :)