Living with ME/CFS is... Having to write down everything, because I will forget it otherwise.
One of the most important characteristics of ME/CFS is "impaired cognitive functioning", such as memory problems. 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.)
Since the ME/CFS I forget a lot: I have to write everything down, otherwise I will forget it again. In the past I forgot things too every once in a while, of course. But then I still knew that I had to remember something (but what again?). Most people will recognise this feeling.
Nowadays it is different, because I forget much more often and much more. And moreover, the whole incident is gone. So, even the memory that something was there, has gone! Especially in the beginning that made me afraid, because it felt like I suddenly had dementia.
This is also "one of the things that goes with it", since I have ME/CFS.