gave her insulin and an hour later she was out of it- she had been vomiting and we hadn't noticed. I took her BG and it was 1.7
Laura, I must have been tired when I read your post above, because I missed that Maya had previously dropped to
1.7.... That is dangerously low, and it means that the insulin dose is
too high. Hypo can be very serious indeed. (A member of this forum recently lost their cat because of hypo. Very sad.

)
I know that Maya has subsequently had some very high numbers, but don't let those high numbers fool you. They may be temporary, and might not show the true picture. Let me explain....
When a cat's blood glucose drops lower than she is comfortable with her body can respond by releasing stored glucose into the bloodstream. It can also release counter-regulatory hormones, the purpose of which is to try to
keep the blood glucose high for a while. It's a protection mechanism.
Sometimes people see high numbers when they test their cat and think that more insulin is needed, but it may be that the reverse is true.
I will check her BG before I give her insulin twice daily.
That's great!

We recommend, for those new to feline diabetes that no insulin is given if the blood glucose (prior to the shot) is below 11. That is to try to allow some buffer of safety.
Also, as well as doing 'pre-shot' tests, it's important to know
how low the blood glucose is dropping. This is crucial.
If Maya dropped to 1.7 it is absolutely the case that the insulin dose is too high and needs to be reduced immediately.
Laura, are you using Alphatrak or a human meter?
I'm guessing, since you're in the UK, that the vet has prescribed Caninsulin? (Please correct me if I'm wrong).
If my cat was still on Caninsulin I would try to ensure that his blood glucose didn't generally drop below 5 (on a human meter) or 6 on an Alphatrak. That would allow some margin for error if, for example, the cat wasn't eating as much as normal, or if he threw up the food.
Caninsulin can start to drop the blood glucose about an hour after the shot, and a cat may experience the lowest blood glucose about 4.5 to 5 hours after the shot (but 'your mileage may vary'

).
Are you able to get tests during the insulin cycle to see what is happening? We really need more information here....
Oh, here's the link to the Hypo document which you may wish to read and then print out and keep handy:
How to treat HYPOS - THEY CAN KILL! Print this Out!!
Eliz