You get so much more than a woo hoo! You get that plus a wowie kawjawie!
Here are some things to think about, when at the vet, the stress alone can induce an artificially high BG say up to 200 points higher than normal BG (some cats actually go lower than higher).
So, let's say the vet visit was 593 - 200 = 393 - still too high a number for a cat.
Now you remove the dry food food and the numbers are 2 something.... not bad, really. Shows that no stress and diet can bring the BG's back in line.
Now you give insulin to help bring the 2 something number to more normal numbers, a few days of insulin and food and lookie, lookie you've got a 59!
And in case you're panicking! No need, if the cat wasn't given insulin and from the sound of it, it's been more than 12 hours since last shot - the cat won't hypo.
What this does mean, is if you give another shot of insulin, you may want to reduce the dose. (Now I don't know which insulin your on - I thought I saw PZI - so, not sure if this is correct protocol for this insulin). I think it is, but not 100%.
Regardless, looks like your cat's pancreas is waking up.
yeah!