Hi Neil,
yes, that's a painful question, I have hasked that myself, although I am not really bedridden (need lots of bed rests in between though) the terror of the moste extreme ME/CFS cases must be unimaginable.
Read the story on the bottom, by Max Rivers: One man's inner experience, and cure :
http://www.cfs-healing.info/index.htmland on the top right : Why did ME/CFS happen to its sufferers? by Anna Harriman.
Both very motivating.
Don't give up!