If you have run into something which looks like insulinoma but then
continually tests out as no blood sugar problem or blood insulin problem
perhaps you should ask yourself if you have any gum or candy around with
the sweetener xylitol that your companion animals may have acquired.  So
far, I have not heard of such cases with ferrets but in relation to dogs
it is documented as a serious and potentially life threatening hazard:
 
>canines who have ingested significant amounts of gum or candy solely or
>largely containing xylitol may develop a sudden drop in blood sugar,
>resulting in depression, loss of coordination and seizures.  "These
>signs can develop quite rapidly, at times less than 30 minutes after
>ingestion," says Dr. Eric Dunayer, consulting veterinarian for the APCC.
 
Remember, there are a number of things which are safe for humans which
are not safe for our four footed loved ones.
[Posted in FML issue 4602]