R, welcome to the nuthouse! As others have said, you're certainly not alone in this.
I don't know why, but that whole "seven stages of grieving" thing applies to people diagnosed with BPD; maybe others too, but I don't have any first-hand experience with those (except AvPD, but that wasn't really anything of a shock). When I was first diagnosed, I did the same thing. Me? BPD? No, that just wasn't happening. Not on my watch. I picked up some books that my GP recommended, I read through them, re-read them, and still, Johnny Cash's words rang true; it ain't me, babe.
Then, as time went by, I'd be out in the world and I'd notice that I was doing something. That's when I'd realize, "oh yeah, this IS Borderline PD, isn't it?" More and more, I realized that I did fit the profile. The realization felt like I'd just taken a Mack truck to the chest.
We're BPD people. One of our things is that we make identities and then cling to them. Unfortunately, one of the first ones that we probably made is the identity of being "normal." It's one of our oldest, and one that we cling to most fervently. Even if we know we're different, we don't like admitting it, to others or to ourselves. Once that illusion is shattered, it has a huge impact on us. It'd be like me waking up one morning and being not only told, but proven, that I'm not actually Johnny Blaze; I'm Jimmy Rocco. I've always been Jimmy Rocco, I just never knew it. It's a lot for someone to digest.
So, the moral of this story is that there are two good things to what you're going through. First, this period of anger and confusion and sadness won't last. You'll settle into your new identity soon enough and get comfy with it. I've even gotten to the point where I call my friends lunatics, but if they say it, I remind them with mock indignation, "that's OUR word.
You can't say that!"

Hey, ya gotta have some fun in life.) The other good thing is that you're not alone. We are here for you. We may not have gone through exactly everything you'll go through, but someone here has probably been through something at least similar. So ask away!
If you ever want to talk about anything, but don't want it going public, feel free to PM myself or MissAli; our inboxes are always open!