I have experienced the "hard to wake" syndrom in several ferrets.  It is
very common in younger ferrets, but I have seen it in older ones as well.
I could be wrong here, since I'm not a vet, but I think someone is feeding
you a line of bull about them going into an actual coma.  I think it's just
more ferret stubborness that keeps them from waking up until they are ready.
I have read about this in a ferret book, also, and it claimed this is normal.
All of my ferrets have always awoken eventually, and never shown any ill-effects
from this.
 
--
M. Todd Hess
 
[Posted in FML issue 0824]