GABA was recommended to me for severe sleep disorder I've had for years. It seemed to work the first night, got about 4-5 straight hours of sleep without waking up hung over. After that, it didn't seem to do anything.
I've gone through periods of the brain fog/dizziness. It seems, obviously, to get really bad if I'm overtired. Are you getting plenty of rest?
I know brain fog is one of the worse symptoms of this whole thing. Hang in there and keep looking!