Scott,
 
Have the vet perform an ADV test and a blood glucose test.  ADV and
Insulinoma could both be at the root of the symptoms you are describing.
The ferret could also have chronic IBD with resulting low blood sugar,
or lympho.
 
Any of the above need prompt veterinary care.  Where do you live?  I'm
sure someone can refer you to a good vet.
 
Anne
[Posted in FML issue 4840]