Hi and welcome to the Chiari forum.
Is that your only symptom or issue since your surgery?
Did you have ALL related conditions to Chiari ruled out? And have you had recent blood labs done to check vitamin and mineral levels as they can contribute to brain fog when levels are low.
Hello. Difficulties with your cognition and memory is really scary. And many will say that it is a normal part of aging. But, with the medical history we have on this forum, I think yours is an important concern. I experience these issues and it worries me (especially when you know what you intended to say during a meeting or appointment, but the thought never came to you). I got a recommendation from a friend of mine to do brain exercises on my computer. If I keep faithful to it, I do feel stronger. There is a fee, but I bought it and am happy I have. The website is www.lumosity.com. They will let you have a trial so that you can see if it is of benefit to you. I hope this suggestion helps you, or that someone comes up with a different idea. There are so many resourceful people here!