First of all, the standard warning against self-diagnosis applies. It doesn't mean that your discomfort or difficulties aren't valid, it just means you could be mislabeling them because of limited information and the inherent limits to self-knowledge. If you haven't been diagnosed with the mental illness you're thinking of but identify closely with the classic description and symptoms, by all means go and get a diagnosis, man.
Anyway, so you've received the news. There's an exhilaration that comes with certain psychiatric labels – bipolars and ADHDers alike are mythically the wild ones, the crazy-creative types and on and on and on. You might also feel relief, finding that that cluster of problems has a name and some promising treatments. I'm not judging, I'm merely speaking from personal experience with myself and some friends.
The exhilaration is okay, to a certain extent. It is true that the wild ones have tended to suffer from the clusters of negative, life-impairing symptoms. The exhilaration is also a fragile form of defense against the stigma that society at large will impose upon you whenever you disclose your diagnosis.
But don't mislead yourself. You have just been informed that you suffer from mental illness, every bit as real and deep as schizophrenia or Alzheimer's, and that your general life conditions will likely deteriorate lest you take the minimal course of treatment afforded by pharmacotherapy.
You'll be taking complex drugs whose behavior is quite unpredictable, and will conduct orchestras in heaven and whiskey bars in hell before your medication (often a cocktail of many drugs) is fine-tuned enough, and even then medications can just stop working at random times, leading to second and third courses of re-tuning. Meanwhile, these drugs will be screwing up your liver and kidneys – and they're your only stab at serving a meaningful, well-lived term as an outpatient in the badly run mental hospital kind of world we're all living in.
What's worse, the medication is just a wrench. The talking cure is pretty much dead – the various kinds of psychotherapies having been proven ineffective in proper trials – but the meds won't fix you. And I hope you're a proud person, because you will have to face the dark side of your mental illness just like every man needs to face the dark side of the human condition. Either ADHD or bipolar could easily lead you to hopeless misery, unrecoverable disgrace or jail– and that's why mad pride doesn't work; that's why the exhilarating side of mental illness just won't do. You'll need to be proud of yourself on your own terms, lest you let your newly-discovered exhilaration run your life.
Know that you have plenty of homework to do. Realize the crazies will not go away. And yes, enjoy the relief that comes with understanding what you have, but don't let yourself be led astray by the vacuous pride of being from the race that produced Vincent van Gogh or John Dillinger. The myths will crush you – only true understanding can help you sort yourself out. Somewhat.