High blood sugar in an animal that isn't able to hold down food sounds strange.

Do you know anyone who's a diabetic that could let you borrow a glucometer? That way you could check periodically to see if the elevated blood glucose remains.

High blood glucose always makes me feel listless and kinda sick to my stomach, too. Maybe your cat has diabetes?
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She was standin' alone over by the juke box, like she'd something to sell.
I said "baby, what's the goin' price?" She told me to go to hell.

Bon Scott - Shot Down in Flames