shaky... underweight,,, lethargic

Question
Hello! I have a few concerns about my baby Nybbyt... I have three ferrets and of the three he is the oldest.  He'll be four on February 9.  He's always had a little stagger in his step that makes him look like a "little boozing ferret" as my roommate calls him, but lately he's gotten to the point where he barely can walk straight.  When held his back legs seem to go a little limp.  He's been sleeping on the bottom of their multi-leveled cage and not moving around much at all.  He's always been a "momma's boy" but when I took him out of his cage and held him, he started shaking all over (more-so than the usual wake-n-shake) and he actually just laid in my arms without moving a single muscle... and as you know... that's very odd for any ferret!  

He's also never really been much over 1.00 lb.  Every time we take him to the vet he's always weighed less than the other two, even though he's the oldest and almost longest.  It's not time for the annual check-up (February) so I'm not sure of his exact weight.  Before the Christmas holidays, however, he looked to be gaining weight, along with becoming more active.  Since we've been back from the holidays he seems to have lost more weight!

HELP!!  I'm not usually one to be concerned over little things, but seeing him lay completely still in my arms (other than twitching and shaking sporadically) I really became concerned about all the signs I put in the back of my mind!
Sorry this is so wordy and long, but if there's any explanation you can think of... PLEASE let me know!!

Answer
It could be a number of things including Insulinoma.  He is so tiny that I would worry about dehydration.  My suggestion is to take him into your vet as soon as possible to have him checked out. Insulinoma may require surgery and/or medication and a special diet so don't delay since the "boozing ferret" could be seizures.  It may not be this, but it is still worth getting to your vet.