Luckily for me my brain fog resolved itself (while I was still on Propecia). I was on the drug for 12 years, missed a week, then went back on and the fog started the very next day. It took about 3 months (during which I had fog every single day) but then simply disappeard (after a weekend of heavy drinking oddly). I do remember having a few shorter incidents of brain fog in years prior now that I know the feeling but at the time I had no idea it was from Propecia. My fog did not include headaches - simply felt like I was constantly slightly drunk.
That experience (plus the fact that I lost morning/spontaneous erections over the past 2 years) scared me enough that I have since quit the drug after a lengthy tapering-off process (which didn’t matter I dont think - my DHT was the same on 0.5mg as it was on .125mg).
So I no longer have mental issues but continue to keep in touch with Dr. Jacobs because I want to keep a close eye on things now that I have quit the drug. I have been off for 5 weeks and it has been somewhat unpleasant so far. I have not run new blood yet but will do so shortly. So far I have not taken any medical action - I am just hoping my system restores itself.