“Brain fog” isn’t a scientific or medical term. Researchers sometimes refer to the experience as sluggish cognitive tempo — a temporary slowdown in your thinking abilities.
When you’re dealing with brain fog, you may have symptoms like:
mental fatigue or sleepiness
forgetfulness
mind wandering
a cloudy or daydreamy feeling
an inability to concentrate or focus
a feeling that you’re disconnected from reality
distraction
loss of motivation
slow physical movement
a feeling of overwhelm
an inability to find words to express your thoughts