Did this follow a virus? If so, disregard.
A little about it a while back.
http://www.pprune.org/forums/showthr...highlight=salt
I happened to see the thing about salt in a European broad sheet. No real science, but so easy to try. A friend's daughter was down to two short days a week at college...sometimes in a wheelchair. She tried salt, and made a steady recovery. Of course, this could have been coincidence, but it was after about 3 years of illness.
Have you tried a brutal illimination of every type of food? One at a time of course! I'm presently going back on bran to aid bowl function, but the first day I'm starting to ache and feel weak.
This will be the third cycle of testing this hypothesis, and so far it's coinciding. Bran seems such a natural food, but if it is the culprit it's so easy to eliminate.