A study showed that the cognitive dysfunction which affects short-term memory, concentration, long-term memory, working memory and vocabulary is actually not due to things like sleep but due to our pain... so this doesn't surprise me in the least bit.

I went to a pain forum a couple of weeks ago & they showed an MRI scan how the brain is affected when in a pain flare, it takes over the cognitive areas of the brain, it's all consuming thus brain fog!

I believe there is a connection between increased pain making cognition go haywire. I've read When you have chronic pain, especially nerve pain like in fibro, it is like your brain is having to constantly multitask and is on sensory overload so of course this makes it hard to focus, concentrate, think, and well pretty much everything else.
Feel better soon 💜

Being in fibro fog is when I realize I am going into a flare.

In a word: YES This keeps me from doing things I would like to that don't require anything physical, just my desire to write, do my photography, even be online. I can't think of words, just simple words, when I am speaking. Sadly, those around me just say "I have that problem too, so it can't be fibro". I keep quiet. Not worth debating. But I do things without remembering having done them, say things without recalling having said them, don't recall conversations others say they've had with me, move from one spot to another without knowing how I got there. At one time, this seemed to be related to meds, but now it is so common I wonder if it is just the progression of the illness. ?????? Hugs to all who have this problem and my sincere support to you, too.