We don't yet know whether Hamlet needs to go back to using insulin. He had a seizure at his strange hour of the night when he has been known to forget to keep regular habits of eating and drinking. It may possibly be that he was dehydrated as that was how he felt when I checked him. I gave him fluids when he had recovered from the seizure, (lasted about 10 minutes), which he tolerated for about 50ml and then declared "that's enough" and refused to stay put. His glucose reading, which we were previously assuming was low at that point in the night time due to lack of eating, was 28.8, (Canadian number), so this is why we are now waiting patiently to get to the vet to check his fructosamine levels. He is still perky, purrs like no other cat I have experienced, and is doing his little walks indoors to make up for the fact that we can't walk him outdoors in the rain and cold.
Hamlet has also been showing a slight limp with the stairs and now that he is back on the phenobarbital, that is exagerated a bit, so he may have arthritic issues in his right rear leg. At the ripe old age of 18 or so, I guess that is allowed.
At this point I am making it a daily routine to check Hamlet for hydration. Since the other night there has been no indication of a repeat performance, so hydration may be the issue rather than glucose concerns.
As Hamlet is starting fresh on insulin and we had previously discussed the possibility of trying Lantus with the vet's encouragement, I am now being taken on a new adventure by Hamlet, which is being recorded on a spreadsheet at the attached URL.