a friends cat 3 year old cat  was ill. She lost weight over a 2 to 3
week period  (although re gained a little too )   and developed
progressive  respiritory difficulty.  She lay about all day every day
for the last couple of weeks  with her little chest going up and down
much too quickly. She had clear eyes, did not vomit, produced normal
looking liquids and solids, had no sneezing or coughing and no nasal
discharge. She did not "feel"   feverish .  She initially did not eat
for a few days and then started to eat modestly.  She drank  a little
more than normal.  He would not take her to the vet despite
encouragement, offers to lifts and even a some money.  Initially for
the first days, I was not too concerned, but in the last week as the
respiritory rate and difficulty seemed to get worse I put much
pressure on him, and visited a PDSA vets to get details of what they
could offer. Well, eventually, the Cats Protection League offered an
appointment at a Vets today.  I visited my friend to give a ride to
the vets and the cat became distressed by being picked up and taken to
the cat and she died 2 minutes later.
Now, she is buried in his  garden, the pathological truth of her
illness never to be known.  I  unsuccessfully suggested that before
burying her we should continue to the vets in case a test might be
possible.

I feel angry of course, my suggestions and sensible proper steps were
not taken.

But does anyone have any idea what this sounds illness sounds like ?  
2 new pets (ferrets, totally unvaccinated or checked by a vet)  )
were introduced to the home a few weeks before the cat became poorly.