Bit of an extreme reaction to safe greens last night Figaro! I guess it’s allowed for first greens in a while. Small aside, we don’t call anything a hypo unless kitty is exhibiting hypo symptoms. Otherwise it’s just a low numbers event, which it technically wasn't last night. Low numbers is below 68 on the AT. We usually reserve high carbs for below 68.
Something that might help you next time you see greens, is to track any extra food you gave, at what time, amount and percent carb. This will help you learn how carb sensitive Figaro is, and what you need to do next time you see a lower number. I used to put it in the spreadsheet Remarks, so I could see how it impacted Neko's numbers.
Good luck at the vet tomorrow. I hope you get answers.

Maybe add anal sac issues to the list? Being in normal numbers for the first time can often feel very odd for them too.