Living with ME/CFS is... Too overlook speling errors.
One of the most important characteristics of ME/CFS is "reduced cognitive functioning", such as problems with processing information. It is one of the criteria which doctors will use to make the diagnosis. (See also the Health Council's advice on ME/CFS, March 2018.)
ME/CFS often causes the processing information to be delayed, so it takes longer to process information. It does not matter whether the information is new or already known.
In addition, people with ME/CFS often have neuro-cognitive problems as well, such as problems concentrating, remembering, orienting, thinking and understanding.
As a language lover I have always been precise on my spelling. That worked out well, because writing texts has been an important part of my work for years. However, since the ME/CFS I suddenly am functionally dyslexic: now I make mistakes in language and spelling, which I never made. And most of the time I don't even see it. A very weird sensation!
Moreover, I regularly can't recall the right word. I know there is a word for what I want to write or say, but what was it again? A form of functional aphasia, which is very impractical. Especially because it happens this often.