I think that there are two possible approaches to this which might work.
The first approach is to do it yourself - keep a detailed record of your wife's episodes which you can then show to her GP. Record her behaviour each time, and if you can take blood sugar measurements or any other measurements record those.
The other approach is to seek professional help at the time your wife has an episode - call an ambulance or ring 111. I guess that you don't think an ambulance is needed, or you would have called one previously.
If you call 111, they will ask a lot of questions about what has happened. What happens next will depend on how serious they assess your wife's condition to be, but they send a detailed report of each call to the patient's GP - it would be difficult for your GP to ignore that.
Personally, I would go the 111 route. If your GP doesn't accept what you have told him already, it might be some time before DIY records will convince him. The 111 system offers a number of advantages - at the very least, they will record everything you tell them, and that will be sent to her GP. Her GP might find that more convincing than your own verbal report.
