This makes so much sense to me. I caught Covid in March 2020 and temporarily lost my sense of smell. I have Chronic Fatigue Syndrome, but at the time it had been more or less in remission for several years. I had an attack of CFS after the Covid infection that lasted about 4 months.
Now, 4 years later, I have an attack every time I’m under stress. And now the attacks are accompanied by severe migraines. Interestingly, I also have ADHD. The medication I take helps with the brain fog, but not with the fatigue or migraine.