Is it possible that your "old-acting" ferret is depressed?  Has there
been a recent change (new home, new cagemate, loss of cagemate, loss
of human?).
 
I agree with Duane that the ferret should go to the vet to be checked out
to rule out any illness or injury that's being overlooked.
 
Take care,
Chana
[Posted in FML issue 4572]