Morning brain fog, constant heaviness, mood swings, and dizziness in a 35-year-old female on folic acid point strongly to a nutritional or hormonal cause. Most likely suspects are: thyroid dysfunction (hypothyroidism causes all these symptoms and is very common in women), anemia (iron or B12 deficiency — folic acid alone without B12 can mask but not correct B12 deficiency), Vitamin D deficiency, or poor sleep quality. Since you're in aviation, irregular shifts and sleep disruption can worsen all of these. A basic workup will identify the cause quickly.