Re: any ideas on this mystery?
Brain fog was one of my main symptoms with neurocardiogenic syncope, I guess it could've also been caused by my tachycardia. I am guessing you have had at least an ekg. How about a holter monitor or event monitor? How about a TTT (tilt table test), that's what they use to diagnose NCS.
I originally was sent to a neuro with symptoms of fatigue and brain fog, and just feel'g like I was losing my cog. abilities. He tested for about a year before he decided just for the heck of it to check my heart. He ordered the ekg and holter monitor and from there sent me to a cardio. The cardio ordered the TTT.
These are just some ideas.