Will a brain fog indicate something serious?

Could be: I would go see a primary care doctor or maybe even a neurologist to see if they can figure it out. You may need to get your thyroid checked out and some of your vitamin levels evaluated. If you feel depressed or anxious you may also experience a kind of brain fog and in this set of circumstances you may want to consider seeing a psychiatrist. I hope you get to feeling better! stay safe!

Hard to find : Scientifically-based articles on this. In my practice the most common cause of brain fog that i see is fibromyalgia. I am including a reference to an article that lists many causes of brain fog some of which would certainly be considered controversial. www.livestrong.com/article/...are-the-causes-of-brain-fog.