I guess I'm in the minority here. We don't have a diagnosis yet, but when we finally got to see a developmental ped and she validated all of my observations, I partly felt relief because finally someone wasn't looking at me like I was crazy, but I've also been feeling more impatient with my son than I ever have. He's 27 months, and we just saw this new doc earlier this week, and it could be coincidental, but my honest answer is that I'm feeling less connected right now and less tolerant of some very typical toddler stuff, eg whining, continuing to do something he's been asked not to, etc. The doc's reaction was not a surprise at all, and I do feel like we have something of a plan for moving forward, but for the moment anyway, that's how I'm feeling, and I'm not sure why. I hope it will pass?
I think the first reaction is usually "yay! a diagnosis/validation," then "oh, crap." Sometimes the latter has to do with actually having an identified problem to deal with, and sometimes there is a let-down due to a vague expectation that things would be "fixed" or "different" now.