Matt, the symptoms you describe Sergeant as having sound like classic
insulinoma.  Hypersalivation, extreme lethargy and "zoning out" are all
symptoms of this disease.  These symptoms are caused by low blood sugar
(glucose) due to overly high insulin production.
 
My recommendation is for you first to read the insulinoma FAQ, and then get
Sergeant to your vet.  Provided the ferret's in good shape, the vet will
probably recommend surgery to remove the tumors from the pancreas, which are
causing the high insulin production.  DO IT!  I had a ferret who went
through TWO of these surgeries and he lived 2 1/2 years with insulinoma.  At
the end he was on medication because he wasn't a good surgical candidate,
but without the surgery he wouldn't have lasted half as long.
 
My ferret was also "3 1/2," but was a shelter ferret.  So he was probably
older.  Once you have had surgery (or, if you insist on not doing it,
medicated), it's a good idea to check the blood sugar once a month.  This
gives you a heads up on possible problems or seizures down the road.  (yes,
if this is not treated, Sergeant may experience seizures.)
 
If you need an opinion (like I haven't stated it?) or have any questions on
dealing with long-term insulinoma, feel free to contact me.  Good luck!
 
Amy & Dave (and their gaggle of giggling ferrets)
RIP Ian and Elektra
[Posted in FML issue 1787]