I've experienced the sleeping-with-eyes-open thing with Illura once, and it
scared the living daylights out of me!  I heard a little squeak, so I went
over to make sure she was ok.  Her eyes were half open, and what scared me
was when I touched her eyelid she had absolutely no reflex.  She was only
breathing a couple of times a minute, and when I picked her up she felt
cool, like her body temperature had dropped.  My heart was in my stomach
until she woke up, yawned, and gave me a lool like "hi ma, what are you so
worried about?" I think ferrets can go into a phase of sleep that's sort of
like hibernation.  Let me tell you that I deeply empathize with your scare!
 
Rachel and Illura
[Posted in FML issue 2991]