My ME/CFS symptoms always followed a pattern of being dramatically worse 5-6 days before ovulation (in addition to getting worse with high emotional/physical stress).
Onset Patterns and Course of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (Chu et al., 2019)
Pregnancy, menopause, and menstrual cycles exacerbated many women's symptoms.
P.S. And a comment from another discussion:
Another example of a leaky blood-brain-barrier occurs in menstruation.
Right before, and during menstruation, the lower level of estrogen causes the blood-brain-barrier to become slightly more permeable. Some have speculated that this might contribute to pre-menstrual syndrome.