I did this with my best friend of 17 years (multiple times) in the span of a year. I was chronically suicidal at the time and I was degenerating fast; doing all manner of self sabotaging, paranoid delusional things.
I keep saying this here. My saving grace was giving into meds. I refused to resort to medication in the first 6/7 months of my out patient DBT treatment and it was a huge mistake. Right after I got on meds (a week exactly is when I felt an impact, although I've been told it takes a month by nearly everybody in my DBT group therapy cohort) Anyway, if your mind is fucked up and you are diagnosed with BPD, I think this will happen to you forever. If you look to your past and you can identify a history of this behavior, then you can pretty much assume this will continue to happen to you, and it's entirely out of your control (AND I UNDERSTAND THAT).
My recommendation to you is to get a med eval and get into DBT training. DOn't go in with a fucked up head because you won't be receptive to the information, and you'll waste a lot of time and money.
DBT. Get there now! and you can look forward to eventually not meeting the criteria for BPD. You will still have it, but you will have changed the way your mind operates and will completely overcome these insane impulses that you have. (THAT WE ALL HAVE). You'll still have them, but you will have great control; greater than people without BPD. You can master your emotions (even the ones that come out of nowhere and prompt you to engage in relationship/career/life destroying behavior.
I lost my best friend. He couldn't stick it out, and I am completely understanding of that. I beat the shit out of him, and drank his blood (figuratively) with all the shit he had to deal with. I've come to accept this reality over time, that he's gone.
I could pick up the phone and call him. After the amount of time that's gone by since he severed ties with me, I am positive he would be open to a conversation with me. But that's in the past.
You have to understand what I'm saying here; this guy was my brother and I sacrificed him day in and day out. I rolled boulders over this dude and did exactly what you're describing on a monthly basis within the last year of our friendship. I know what you mean by losing control and getting carried away by the momentum of irrational stupid decisions AND NOT BEING ABLE TO STOP, AND NOT KNOWING WHY YOUR EVEN DOING IT SOMETIMES. This is what happens to us (DBT peeps). It's fucking horrible and that's your life--until you grab the reins and get control. You should take the advice above about DBT and med eval. The meds are just to get you to stabilize. If you're already on them, then they are not working for you and you need to experiment with something new and not be afraid of trying this stuff. It's scary; I've had some really bad experiences when we were calibrating my load out, but it completely saved me from damaging my life further.
The reason I don't think they are working if you are on them is that it becomes much more difficult for the paranoid thoughts/delusions/anger, etc. to take control of you. It still happens, but drastically less, and it feels a bit out of character if the meds are being effective for you. Keep in mind I was completely insane (and by that I mean paranoid, delusional, irrational [which I confused with logic, as everything I was thinking seemed to make a lot of sense to me] and I was suicidal for a reason that I reduced to an extremely cut and dry explanation that nobody could understand. I hit the bottom and was in bad shape. The meds turned this off almost instantly as I said and it was a very small dose. 10mg prozac. So you shouldn't be having these instances that spiral as hard as this from my own personal experience with BPD (but alas, everyone is different) This is just my suggestion/advice. Take it or leave it.
Okay, so accept that this is the situation. You fucked up royally. You have guilt--and that's great btw because it means you know you violated your own values. Sit with that. It's uncomfortable, but let this pass over you. It will totally pass.
Do not attempt to contact said person you just annihilated with your monster. Let some time pass. If you want, you can send a short one line text apologizing, but don't anticipate to repair anything today, or this coming week. Depending on the severity of the shit storm you brought down upon yourself/everybody, wait for up to 3 weeks. You need to get over the guilt first, accept the situation, and then attempt a repair. For this, I would suggest reading up on some DBT skills around interpersonal relationships. GIVE skill is your go to for this. give it a week. Get your head right. then start looking into this information and compose a letter that will hopefully get this person primed for an official apology over the phone or in person.
You CAN totally fix these fucked up situations you create (conditionally and within regard to context), but understand that if you continue to repeat these behaviors with this person (if this is not the first time) there will be such a large emotional withdraw/debt that eventually they will cut you out of their life completely and the sincerest apology will not get through. Get some rest, let a few days go by, and proceed with a repair.
Additionally I would go for a walk, or a run if you can. Try and get some exercise and sleep WELL. This may sound asinine, but this will help you get through the guilt/wave of emotion you're having and accept reality (of the situation you created and the resulting consequences). YOU NEED TO GET THROUGH THIS BEFORE ATTEMPTING THE REPAIR and this will speed up the process.
Find a DBT clinic in your area and take back your life! Fuck BPD, I can't believe I have this shit either, but I do; that's the reality. You gotta own it and do the work, or you'll be fucking yourself over for the rest of your life. You can absorb the lesson from this one since it is impacting and terrible and hopefully it reminds you to stop yourself when you get on a crazy roll. You can stop.
I just read your follow up comments and by your language it sounds like you might have some experience with DBT. Lean on that. DO the work.
It really helps me to write about this stuff. I can see how far I've come. Thanks for the opportunity to share my experience/opinion with you. I hope it helps.