I had been suffering from a blocked nose, daily headaches and sinus
pain for over 18 months, had been to the doctor numerous times,
initially diagnosed with sinus problems, referred to an ENT specialist
and eventually had a sinus op to remove a nasal polyp.  Still no
success, particularly with the daily headaches.  Went back to the docs
and was prescribed various other meds including propranolol and then
when that didn't work amitriptyline.  Then one day my central heating
boiler broke down and I got the engineer out to fix it, during this he
did a 'smoke test' which he said was not extracting properly and he
said he needed to go into my loft where the flue was.   The first thing
the engineer said to me when he climbed into the loft was "have you
been having headaches ?" when I said yes he said he had found the
reason why -  he had discovered that the flue (which goes out through
my loft) had broken and the carbon monoxide fumes had been feeding down
into the house.   Anyway he fixed the flue and within 48 hrs my
headaches disappeared.  The first thing I did was go out and buy a
carbon monoxide detector for the house and I am monitoring this very
closely now!  A number of thoughts occur to me:

    a.   I have been very lucky that the fumes were at such a low level
otherwise I would be dead by now.

    b.   At no stage did any of the docs I see even suggest any sort of
poisoning.

    c.   I have been through a needless sinus op.

    d.   Although I was shocked that it was CO poisoning I am just
delighted to be headache free for the first time in 18 months.

I feel fine now but did go back to the docs to explain what had
happened - the doctor didn't seem particularly clued up on CO poisoning
and just said I should be fine as long as I wasn't exposed to the fumes
any more.  I do wonder though if there will be any long-term effects.