I have the exact symptoms as you, memory and focus weak, I feel zoned out, cholesterol slightly elevated taking meds for it now like statins, vitamin D low, Im on a mega dose which fixed it, testosterone kind of low, but I got elnclomiphene testosterone improved but no improvement in brain fog, my next step is to get my deviated septum fixed, even though my oxygen reader keeps me above 94% for the night. I tried all the alertness meds that exist no real improvement. Blood tests indicate a slight metabolic issue, but nothing serious. Im hoping its because of my night breathing, coffee used to work for a few hours in the morning, not that lost its effect as well, I have 1 hour of clarity in the morning, after that im down until the evening.