I was OK until I got a desk job and quit exercising, oh and middle aged wear and tear on my back. With mental fog, one thing to consider is if you are getting a metabolic disorder, which would show at some point in your lab results – blood tests. This is resolved with regular diet and exercise, or medication in some cases. Anxiety and depression will also ruin focus. Another consideration is personality traits. People who are naturally lower in trait “enthusiasm” may not be so energized by many activities, especially once the novelty wears off, and they don’t focus. If they are also introverted and ADD, well then… Maybe time for an adventure vacation with lots of hikes. In Canada you could try low strength marijuana (5%), 1:1 THC to CBD, or if it is legal where you are. I just tried it for the first time with legalization and it definitely energized me, helped greatly with sleep and I had more focus the next day. I only used it in the evening at home. It does not replace prescription medications but helped a lot when the meds were not.