Fibro Fog as they call it, is also know as Fibromyalgia fog which effects your memory and can cause word mix-ups and difficulty with concentration.
When I first started to experience it I thought it was due to a particular drug that I was taking for my pain and Fibromyalgia, so I cut down to the lowest dose but that made no difference whatsoever.
Some studies say that it is caused by sleep deprivation which is very common in Fibromyalgia, but others found that poor sleep was not the case.
Additional research though not on Fibromyalgia specifically shows that chronic pain itself may affect the brain. A technology called functional MRI found that in people with chronic pain, a front region of the brain mostly associated with emotion is constantly active. The affected areas fail to shut off when they should, wearing out neurons and disturbing the balance of the brain as a whole.
They suggest a number of cognitive treatments to try to help with this but I find the best is to just ‘pick your best time of day’ to get your jobs done. You soon know when your at your best which for me is either first thing or immediately after my afternoon rest. If I miss my afternoon rest then I know I may as well not bother trying to do anything that uses my brain much, like writing interesting blog posts :))