Disclaimer: I realize that there are a ton of pseudoscience claims about cider vinegar out there. This is purely my own n=1 anecdotal experience, I'm not trying to make any broader scientific claims.
I recently tried raw (unpasteurized) cider vinegar to see if it would give me any probiotic benefits (diluted in water of course, I'm not an idiot.) To my surprise, I noticed that shortly afterward I felt a mild stimulation and was a little happier than usual. I have tried it several times since then and gotten a similar result.
To see if it was just an effect of the acidity, I tried the same thing with pasteurized cider vinegar and I felt no change in mood or mental state. I realize that this is not exactly a blind test, but I thought it was an interesting result nonetheless. I think it would be difficult to achieve a truly blind test since raw and pasteurized vinegar taste noticeably different.
Since raw vinegar contains live acetic acid bacteria and their fermentation products, my theory is that this effect is either probiotic or enzymatic in nature.
If you want to test this out yourself, just mix 1-2 tbsp raw cider vinegar (e.g. Bragg's) into 12 oz water. If the taste is not to your liking, add a sweetener of choice. Be sure to rinse your mouth with water afterward, the acidity is not great for your teeth.