Jonathon's blood sugar spiked last night

I took Jonathon to the vet because he has a fairly large sore on his side.  For about a month, his blood sugar was between 70 and 131.  The vet told me that she considered him to be transient, meaning his diabetes had gone away.  This can only happen in cats and vets don't totally understand why or how it happens.  

So, for about a month, he was not receiving insulin.  When we were at the vet, the vet told me to stop testing him everyday.  I could now test him 3 times a week.  Last night, I tested him and his blood sugar was 235.  Two minutes later, I tested him again to make sure the machine wasn't malfunctioning and his blood sugar was 266!  I was concerned because it was so much higher than usual and because it went up so much in 2 minutes. 

I called the emergency vet and asked them what to do after the first two times I tested him.  They told me not to give him insulin because it could mess him up since he has been regulated for so long.   I tested him an hour later and it was 257 and I wasn't so worried anymore because it went down.  

He wasn't acting strange so I didn't think that the higher blood sugar was causing him too much trouble.  It was definitely a shock to me though, I have become so used to him having a low blood sugar.  I am going to call the vet today and see what they want me to do.