I would just do what you have to until you see your doctor, but you need to go prepared with literature explaining what phenibut is and why baclofen is needed to switch and taper. Baclofen is not a controlled substance in the us, as someone speculated above.
I would try to stay calm and its not likely you are going to die. On the other hand "captain kratom" from the internet does not know with certainty that death from phenibut withdrawal is impossible. Its a very new drug in the grand scheme of things and if you feel you absolutely need medical help at some point, get it. I can't help but think a large part of this is psychological because you are really getting yourself worked up, but (not to detract from baclofen as a completely safe solution to this) there are documented deaths from sudden baclofen cessation at extremely high doses and a major symptom of baclofen withdrawal can be low blood pressure. I mention this because baclofen is the closest related substance with a long history, but its perfectly safe when tapered properly. Again please don't let this add to your already paranoid state, if you really are having an attack of low blood pressure, it should be confirmed with a vitals check and real symptoms. (Your perception of small veins and feeling slow isnt enough).
Go to Walgreen and get a blood pressure reader if you're that worried about it. I think one of the best things you can do for yourself is try to calm down and stop smoking so much. make sure you go to your doctor prepared to explain what phenibut is and that it's a gaba b agonist because they will have no idea wtf it is, just like they wouldn't at a detox center (they didn't at one I went to).
Just keep on with as little dose phenibut you need supplementing with as little dose Pentins as you can to make it til you can see your doctor and explain things to him (I did similar although it was as low dose as possible with small amounts of clonazepam to stop the reversed effects until I could get to my doc.) It's really as simple as your dependentant on this weird ass gaba b agonist and have read of others being successfully transferred to the gaba-B agonist baclofen and weaned. Baclofen is much more potent, although you should look up a conversation rate if you can find one. I think it ranges around 5-10x potency because I was switched to 60 or 80 mg a day from around your dose of "but". You're gonna be ok buddy just hang in there, stop smoking so much and try to gauge what's really happening from what's paranoia induced.
**I think these "reversed effects" we experience when it turns suddenly is like an instant exciteotoxic rebound brought on by the suboxone and likely in your case nicotine. Sort of like when you put your thumb over a hose and the water sprays (the phenibut being the thumb, the water being glutamate, dopamine, etc). Noy very scientific sounding but there are studies that show gaba b agonists increase these neurotransmitters (likely downstream) at low doses (or tolerant doses in your case) while blocking them at higher doses. (Just google baclofen effect on dopamine and pubmed results will come up)
Again good luck and try to chill you're gonna make it bud