I have been testing this now for several weeks, and it is working very, very well. Nobody has asked me for more information or to explain AND BEST OF ALL. People have responded by being patient and understanding.
I have symptoms such as not being able to think of a word, mixing up my words, stopping altogether, pausing, and stammering when talking. I also have problems with short term memory.... like sometimes about 10 seconds after I'm told something!
I now say this the moment after I recover following one of these symptoms, before they have any opportunity to respond: "Please excuse me, I have a brain problem (or sometimes I use the words brain condition or just illness) which causes me to have difficulty talking/with my memory (whatever fits the situation). I never know when it's going to happen. Please be patient with me."
So far, everyone has been extremely kind when I say this. I find that people are far less kind when you say words like Fibromyalgia, M.E., chronic pain, fatigue, memory problems, etc. I think this is because people understand that when the brain is messed up, you can't do anythng about it, and that it doesn't mean you are a scrounger. Maybe they are terrified of losing their brain function, too, which could definitely help with the sympathy. If you just say 'I have problems remembering things' or something like that, they invariably launch into something like, "Oh, we all do when we get to a certain age." or telling you their latest memory gaffe.
I don't know about you, but lately when I use the word Fibromyalgia, people seem to want to tell me about somebody they know who 'claims to have fibromyalgia or CFS' but who they are sure is cheating and just using that as an excuse to be lazy and get benefits. Their contempt of the condition and their skepticism will be obvious when they start in like this. It's hard to deal with and there is no way you are going to convince them.
If you decide to try what I am doing and use the words 'brain condition, brain problem,' etc. I would be interested to know how it works for you. As I read more and more about the changes in the brain function of Fibro sufferers, I realize that giving that as a cause is probably even more valid than using a name for your illness like 'fibromyalgia', which as one wiseacre informed me, "just means pain in muscle tissue" as if to say it's not a reason for all I am experiencing.
Best of luck to all of you as you struggle with other people's perceptions and reactions to your illness.