As for brain fog. Yes this has happened. He forgets what he was saying or doing. But it's not an old age thing. He sleep walks and appears totally lucid when he does it, except that the situation is inappropriate for the middle of the night.
It really sounds like he is a Vestibular patient. You can do the searches with a search engine Vestibular disorders +anxiety. There is a lot more information out there than what I had in 1994.
I also very highly recommend the book "Phobia Free" by Harold Levinson. Don't let the title throw you off. In that book he puts the Vestibular triggering anxiety puzzle together. He is a Neurologist and Pyschratistist and was decades ahead of his time.
BTW I bet he can wear out a good pair of shoes pretty fast huh? Breaks over the sides unless he wears corrective insoles? That's due to walking of balance it makes the ankles turn in real bad. Concrete floors are the worse. I also have to use a cane now.