Thank you all for you responses. I am glad to know I'm not alone. I didn't think it was possible to have hypo symptoms with diet only control. It will be interesting to see if they fade with time.
I hadn't thought about blood pressure, I do have a monitor so I'll check my readings next time.
My low sugar feelings resolve after I've eaten something, I'll feel OK after about 10 minutes, I feel like I absolutely have to eat something or I'll die, which sounds dramatic.
I did ignore the symptoms last month as they happened when I was cooking dinner. I ate dinner then fainted. My partner called an ambulance, they checked me over and my blood sugar was 8.2 (about 30 minutes after finishing eating) so they were dismissive of the faint being caused by that and told me I'd had a panic attack. My ecg showed tachycardia, my GP wasn't so keen to dismiss it as anxiety and thinks I'm dehydrated, so the electrolyte suggestion is very interesting.