Low carb may be the culprit. We need carbs, those that get to few can have those symptoms. Our brains dont function properly if deficient.
Age plays a role, along with hormonal balances. As we age, our dietary needs change. This varies form individual to individual.
Coconut oil has been shown to act as carbs in the body, Although it is saturated fat, it does not cause problems, being it is plant based.
Maybe try to incorporate this into your diet.
I will follow this post in the event you have questions, or PM me and I will reply.