i want to add a few things about medication i've taken against anxiety in general:
they shouldn't be a first line drug, but for me, when a panic attack hits there are few options, and all of em GABAergic: benzos ('specially the anxiolytic benzos are best for the immediate relief from something like this. alprazolam is my favorite for this purpose.). alcohol works too, on a very sloppy, primitive basis, and yeah, fuck alcohol.
GBL/GHB are also really, really good in this regard, but they lose their anxiolytic properties faster, and are highly physically addictive. i've never had a full-blown benzo addiction, but today i went to ER for the very first time in my life because i'd relapsed with alcohol, and together with the GHB i stopped abusing it formed an overlap of all-around misery. the two days trying to pull this thing off cold turkey was by far the worst in my life.
but when i first started getting diazepam at the age of 17, it was something like 10x10mg and that lasted easily for 4-6 weeks. back then i saw them as a medication, admittedly a pleasant one, but they were tools more than inebriants to me, i used them either . with this small amount i got by okay. back then, 10mg would usually do to stem a panic attack. that lasted for a bout a year. in that time frame it worked wonderfully, because even though i enjoyed its effects to some i hadn't breached the barrier yet, there was then my mother was diagnosed with terminal cevprescribed icular cancer and my benzo use changed so quickly. instead of using em like they should be used, i started using them as a coping mechanism. my prescription in those days was 20x1mg flunitrazepam and 50x1mg alprazolam. and that was a combination i sticked with for quite a while.
before this started, i'd do 3mgs of flunitrazepam over the coarse of a few hours and felt fantastic. however, then my mother died, i was there to watch and had no coping mechanisms. and this was the start of my addiction, which came precariously close to full-blown dependence.
after that i still got (semi)-regular scripts, but also bought substantial amounts of flunitrazepam and diazepam on the black market and that was a fucked up time.
anyway, benzos are really, really useful drugs if you can use them as they should be used. if i haven't had any in a while, and i get one of these jet-black panic attacks, nothing deals better with it than 3-4mgs alprazolam.
all in all, benzos are drugs that for certain people like me, with their plethora of anxiety issues are invaluable. my problem always is that i also enjoy the care-free, laid back feeling they give me so from a script at least a third will be used recreationally.
other anxiolytics i've tried:
pregabalin: takes quite a while to kick in, so it's basically useless for panic attacks, although they largely have replaced benzos for my agoraphobia, because then i can plan ahead. take whatever amount will give you a decent anxiolysis, and that effect is really long lasting. tolerance builds really fast. i can feel a good dose (1200-1500mg) for hours on end. now this is not a safe or recommendable dosage, as someone unfimiliar to both pregabalin and gabapentin, start slow. for gabapentin i'd say 300-900mgs should do, while with pregabalin 75-300mgs. it's a useful drug, but for me it lost it efficacy after always about 2 weeks after a dosage uppage. keep in mind that these are rough estimates based on how a variety of friends i introduced them to reacted. and in terms of effect i've never encountered a class of drug where the opinions are so far apart. daily use never worked for me (900mgs pregab a day for 6 months) and (3600mgs of gabapentin a day), it seemed strangely similar to benzodiazepines to me. gabapentin has a more mood-elevating effect, while pregabalin is much more anxiolytic. the latter works well for me on a take as needed basis.
i took grams up grams upon grams of valerian root during the first day of withdrawal, because they seem to have mild effects on the GABAa receptor. this may work for people whose receptors are pristine, some of it may be placebo effect but i fucked my whole GABAergic system pretty constantly for years. this might help you if your neuronal plasticity isn't as warped as mine.
promethazine: one of the first (maybe even the first) antihistamine. it's sedating, very mildly anxiolytic and good for sleep. beware though. at higher dosages it develops (albeit slight) antipsychotic effect and after taking way too many because i couldn't sleep, and after having ingested about 300mgs in eight hours i for the first time experienced the horror that is tardive dyskenisia. it wasn't even fairly strong, more constanct muscle twiches but it was incredibly fucking annoying and if such a relatively weak secondary antipsychotic produces shit like that, i cannot even imagine what haloperidol or chlorpromazine would do.
chlorprothixene: atypical antipsychotic and along with promethazine used extensively in germany as a sedative/hypnotic. taking a low dose during a panic attack amplified it tenfold.
this is just about all i can think of right now on the subject.