I was sorry to hear about your loss.  Ferrets, due to there small size,
has very little physiological reserve when they get ill.  They can get
dehydrated, sick, and even die, within a matter of hours.  My wife and
I have had several ferrets get very sick very quickly, even with simple
things like stomach viruses.
 
Having owned ferrets for going on 9 years now, my advice to all ferret
owners is this: If they look sick at all, especially lethargic (because
they are NEVER lethargic)-i.e. droopy- it is much better to take them
to the vet sooner rather than later.
[Posted in FML issue 4116]