Hello, I'm Dr. Kara. I have over 20 years of experience as a veterinarian and I'd like to help with your concerns about your little one.
The symptoms he is displaying and his response to treatment with honey are fairly classic for an insulinoma. I do recommend a urinalysis, full blood count and biochemistry panel though as other causes of low blood sugar, including liver disease and a severe infection need to be looked for as possible causes as well. I also recommend these further tests because we want to be aware of other health issues if they are present as it may influence how we choose to treat him.
It may be difficult to see insulinoma tumor(s) on the pancreas, especially for someone that isn't used to looking for them. In most cases however we don't need an ultrasound for a diagnosis, although it may be helpful to evaluate him for metastases to his liver, spleen and lymph nodes. We can usually diagnose an insulinoma however by the symptoms and if his resting blood sugar is less than 70mg/dl.
I understand that you are taking him to a specialist tomorrow, and they will certainly help with diagnosis and therapy options, but you need to keep him stable in the meantime.
You should be feeding him a high quality food high in protein and fat and low in simple carbohydrates in small amounts every couple of hours to keep his blood sugar levels consistent. If he becomes symptomatic it is OK to use glucose sources like honey or karo syrup to quickly get his blood sugar up but as sugars stimulate insulin release in general we want to avoid them. Try to keep him quiet and keep his stress levels down to reduce calorie needs.
Please let me know if you have any further questions.