The behaviour you describe I have experienced with only one ferret.
It began suddenly at 5 years old and was used persistently, Sue tried
repeatedly to drag me into her favourite daytime sleeping spot. It
became so intense that I began to think that it was a kind of
'mothering' behaviour brought on by adrenal problems. She would take my
finger crossways in her mouth behind her canines and take a firm grip
without drawing bllod and then drag me to a cupboard (this is her route
to her favorite daytime sleeping den - the top drawer). At this point
she couldnt get me any further but just pulled and pulled, I extracted
my finger and you could see her practically stamping her paws with
frustration and hissing like crazy.

I took her to the vets for a Tennessee panel but the results came back
normal.

About 2-3 weeks later she developed a swollen abdomen and blood tests
and ultra sound did not reveal any obvious problems. As the ascites did
not subside after a course of antibiotics the vet and I decided to do
an exploratory op. What was found really shook me, almost the whole of
her liver was a large blood filled tumour (hemangiosarcoma) with only a
small sliver of normal pink liver remaining. The vet called me in to
see what he had found and said it was inoperable and we decided to let
her go there and then. It was a shock as right up to leaving home for
the vets office she had behaved normally, playing with her cagemate,
eating and drinking as usual. she had never shown any symptoms apart
from the ascites and trying to hide me away.

This is not to suggest there is anything at all with your Blacky, just
that sometimes a sudden behaviour change can have more meaning than we
think. My newest ferret Suki 11 mths old really loves to play with her
teeth and my hands and I hand wrestle her as you do but she sometimes
misjudges the pressure needed to get my attention Ha Ha !.

Tony (not a vet), Sugar and Suki.
In memory of Sally and  Sue.

[Posted in FML 5579]