Sorry Nosher, I missed your reply.
Yes, I test at various times throughout the day, not just post-prandial, and I did test after I was diagnosed and found that my BG during those post-breakfast dizzy spells was 14-16. I was also quite hot and sweaty during those bouts too.
By experimenting with what I ate for breakfast and quite a bit of testing, I found (surprise, surprise) that breakfast cereals, even without added sugar, weren't at all good for me and the worst one was rice crispies, which gave me a reading of 18 on one occasion. Once I stopped eating those, my mid-morning BGs fell and have been under control, ever since.
My HbA1c and fasting BG haven't been bad for quite a while now and they've recently dropped again (although if I eat the wrong things I can still register an 11, 2 hr after the meal), as I've managed to sustain a bit of weight loss and do far more exercise. To be fair, they weren't that bad when I was diagnosed, but lowering them since has sorted out most of the symptoms I'd been having for a year or two beforehand.
I'm due back at the GPs later this week, for the results of my latest blood test, and I'm intending to see what he thinks I need to be doing, longer term.