One possibility is that the Caninsulin may not agree with her - or possibly the dose is too high and her body's having to work hard to counter it. (Pure conjecture on the latter - impossible to know without BG data but it is a possibility which needs to be considered for safety reasons.)
Saoirse was OK with the Caninsulin injections for a little while after she was diagnosed (she had very little energy at that time anyway) but not before long she started trying to find the most out-of-reach place possible to hide when it was time for her Caninsulin dose in order to avoid the injection. She also started growling and sometimes hissing at me; highly abnormal behaviour for her.
When Saoirse was switched to Lantus the growling, hissing and hiding all stopped. She has never been overjoyed at getting injections but nowadays she'll whinge at me sometimes when I'm administering her dose - but she still sits patiently and waits for me to give the injection to her; no attempts to avoid the dose. That would never have happened with her on Caninsulin. Saoirse is a much happier cat on Lantus. The difference is like night and day.
Did you mention that you were worried whether Smiffy was unusually lethargic lately? If yes, then I suggest you look at the posts from member Sandrine and myself about clinical signs to look for which could give you some insight into whether the Caninsulin may be disagreeing with Smiffy. If anything there chimes with how Smiffy is behaving let your vet know. I think it advisable to call your vets regardless to let them know that Smiffy is getting very fractious when you're trying to administer her Caninsulin. They may have helpful things to suggest to you.
Mogs
EDITED TO ADD:
Dingbat here neglected to put the thread link (beyond exhausted - brain a bigger mess than normal):
http://www.felinediabetes.com/FDMB/...orse-symptoms-not-due-to-hypoglycemia.153310/
Have a read through of the posts on the above thread, Looby, to see what signs to look out for which might indicate Caninsulin itself may be the problem. Not all insulins agree with all cats.
M
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