Cognitive impairment is the most 'damaging' symptom of ME for me. I can't organise things in my own head enough to get things done - a simple (and i do mean simple - but one step up from beans on toast) recipe can take me months to get a day where it's possible to even attempt let alone be edible - and of course the process of doing a 'new' thing, even badly, probably especially badly, often crashes me for a considerable time.
That's simple everyday stuff, more complicated stuff - I can;t even organise my thoughts well enough to put down notes/fragments so someone else can help me with things - things currently that need doing are summary of a couple of conditions for GP - to get referred - notes for PIP questions so someone can help me to turn them into answers etc. (that one's been going on for years).
So, CI stops from doing things, or even being capable of doing enough so someone else has a place to start in asking pertinent questions so that they can help/do things for me.
It is the thing that is most likely to do me serious harm.
Obviously day to day it's PEM, pain, fatigability and of course sleep issues. GI issues recently reared their ugly 'head' again, all severely limiting what I can physically do - but the thing that's causing me the most worry/concern, and is likely to cause me major issues, impacting on other symptoms, and, probably irrelevantly, having been costing me around half the income I should have had over the last several years, and likely to cost me roughly half the income I currently have, is cognitive impairment.