It is almost impossible to describe the feeling of not being able to think in this way. I'm a senior software engineer at a large company, I spent much of my time diving into different code bases, and in meetings where I am often unfamiliar with the specifics of a situation and need to quickly reload context. When I am in a state that I have brain fog, I absolutely cannot do these things - I need to sit and prepare for a meeting, and even then I can't think quickly enough in it to be able to comment on anything in a meaningful way. Creativity is not possible, I can't think around a problem at all. Understanding unfamiliar code becomes extremely taxing (if not impossible). Whilst I'm not as bad as some of these folks that are described in the article, coherently forming sentences how I would normally (I'm someone that "thinks out-loud" often) is just not possible. It's debilitating.
For folks that don't have it, it can be hard to explain. Like someone in this article, I tend to just cancel things when I'm in this state (which can be for days, or weeks -- luckily I get to emerge as my body deals with being able to eat again). I just need to sleep - partially because of the emotional toil of the frustration of being cognitively impaired overnight, but also from the physical toll having a flare-up causes my body. I'm not really making this post (and sharing things that I probably usually wouldn't) for any reason other than to just say to folks, hey - be understanding to your coworkers, these conditions are poorly understood, and difficult to deal with. We all tend to feel guilty for not pulling our weight during the time that we're sick, so sometimes just knowing that our coworkers are cutting us some slack really helps :-) Thanks!