Where does the "foggy thinking" or inability to concentrate come from with thyroid problems?

Yes: It is possible to have hypothyroidism which means low thyroid hormone. One symptom may be clouded thinking. Other conditions may cause similar symptoms and not every one with hypothyroidism has clouded thinking.

Slowing down!: Diminshed thyroid function keeps the brain from adequately sustaining the energy (glucose)-consuming processes needed for neurotransmission, memory, and other higher brain functions.