ME/CFS can definitely cause terrible memory problems at times. They're usually much worse when you're tired or in a crash. And it can be terrifying to realize that parts of your day, or even an entire day, are a blur or are completely absent.
I had neuropsych testing done after becoming ill because I felt that my mental capacity was so diminished. My overall score for the attention and memory section of the test was in the 50th percentile (significantly lower than my other scores), and some of my subtest scores were as low as the 25th percentile
. I work with students who are diagnosed severe disabilities, and many of them have higher scores than I do!
However, on a good day when I have a lot of energy and my brain is working well, for the most part my memory works like it should. And if I work hard to get information into my long-term memory, it stays there. I have even managed to slowly memorize some poetry since becoming sick!
But like @nyanko_the_sane
pointed out, there are good strategies that can help us remember more. Taking pictures or jotting down notes are both great ways to prompt memories. My room is covered with little sticky notes, even for little reminders like "You put a pot of water on the stove. Check it at 12:20." These little reminders can help memories surface.
I am also much more intentional about trying to remember pieces of information I know I have a tendency to forget. For example, when I was leaving my apartment I often didn't remember whether or not I had locked the door, even after taking just two or three steps away. So now focus really hard as I put the key in the door, and I say out loud "I am locking the door, it's locked" as I lock it and feel the knob. Then I take one more moment to focus on remembering before walking away. Being more intentional about trying to remember and engaging more senses by saying something out loud does seem to help.
My diminished memories and cognitive abilities have scared me at times and frustrated me at others. But over the years I have been able to work out strategies to help me remember more.