However, I have upvoted you because I agree that probiotics can play a part in coping with anxiety for some people.
I have experienced anxiety attacks for the last several years (including several full on panic attacks). For several years before the onset of the anxiety episodes I have also had IBS like symptoms (which continue to this day). I have noticed a clear link between the two (anxiety accompanied by nausea and frequent trips to the toilet). I could go into the disgusting detail but I won't.
To cut a long story short, I have found that consumption of high dose probiotics containing B longum has corresponded with a decline in sympton severity & frequency [1]. I am not suggesting that this is a cure (or that it will help all anxiety sufferers). Other things that help are reductions in caffeine & alcohol intake, increased exercise (the more extreme the better) and acceptance of the physiological symptoms of anxiety - it is easy to think that heart palpatations etc caused by anxiety are a result of genuine physiolgical issues (which in turn causes more anxiety).
[1] https://www.researchgate.net/profile/Robert_Lalonde/publicat...
Not just any probiotic - there's a lot of unresearched crap being sold, some even dangerous (e.g. some soil based organisms can become opportunistic). I can recommend L. Plantarum 299v (this strain reportedly does not produce d-lactic acid, which is really desirable, as probiotic use could lead to acidosis [2], [3]), E. Coli Nissle 1917, and maybe a well researched soil-based mix (Prescript Assist maybe, they claim that it's the best researched probiotic in its class). Testing your biome at ubiome could provide you with info on what is missing, or what group of organisms is underrepresented. I haven't tried that yet though.
Sorry for not providing links to studies for all my claims, as I'm not at home, but all that should be easy to back up by searching at pubmed.
[1]: https://www.ncbi.nlm.nih.gov/m/pubmed/23384445/
[2]: https://med.virginia.edu/ginutrition/wp-content/uploads/site...
[3]: http://hkjpaed.org/pdf/2006%3B11%3B246-254.pdf
Update: Added another link. Why the downvote?