I too am 75 and had been running out of gas for years in the late afternoon. Enough so that my GP ordered cortisol tests 4 times over 24 hours. The results were surprising! 3 of the 4 were in the normal range, except the late afternoon test. It was almost non existent at 12% of normal.

The diagnosis was Adrenal Fatigue!
Because I had had 10 + years of unmanaged Celiac Disease gut damage, my native ability to generate the normal body’s antihistamine DAO was destroyed and as a result my Adrenal glands were overwhelmed and cortisol production was negatively effected! Initially the treatment was go gluten free immediately and to increase my B12 and/or dermal applications of Cortisone via adhesive patches later in the management approach.
Results: still use all three methods to minimize the inflammation that triggers histamine and my immune symptoms subsequent attempt to stimulate more cortisol production. Not a cure, rather a way to manage an ongoing issue!
Chris47 -