I hope I've not missed something here and I genuinely apologise if I've got it very wrong but my understanding from looking at regular coke is that it contains about 10g carbs per 100ml, which makes it just the same as fruit juice (although I do realise it's different types of sugar etc).
working on the basis that 10g carbs = 1 carb portion = bg increase of 3
.
Even if you did end up with a pint of regular cola and did drink it thinking it was diet cola,that would equate to 5 or 6 cp = BG increase of 15-18. To have your bg at 30+ then you must've already been quite high. surely if you're checking your sugars levels regularly then you'll spot this very quickly?
like I say I don't know, I've not been on DAFNE and despite being t1 for a very long time, i have had extremely little education about how to work it so you guys probably know a lot more about it than me.