I don't know if any one else has come across this article.
My wife found it through another website and just in case it hasn't been mentioned here I thought I would post the link here.

http://www.butyoudontlooksick.com/articles/written-by-christine/the-spoon-theory-written-by-christine-miserandino/

It explains how Christine, a Lupus sufferer, found a way of explaining what it is like to have an invisible or chronic illness.

I hope someone finds it useful.

Hi Mathsman I like this analogy and will use it as many of my friends don't see "through" how I "look" -particularly on a good day or when I borrow a spoon from tomorrow and it means I don't function with less spoons but hide away so no one sees

This really explains how it is like. Thanks.

An excelllent theory, but rather long-winded. I think something more desirable than a spoon would be more effective, as the listener would be more upset to lose it. Useful, nonetheless. Thanks.