As you are not on any medication then I would say it is not usual to feel rough over a few minutes. However it can happen if people have eaten quite a high carb meal and their pancreas gets over enthusiastic and over produces insulin and levels drop quickly making you feel unwell. I would have a word with your nurse but in the meantime keeping a food diary to see if you can pin point any thing that could be causing it to happen, like a high carb food would help.I posted a couple of days ago about my first Hypo, I am now wondering if after feeling fine all day, does going from feeling OK to being wiped out in 15 minutes seem the normal trend?. It just concerns me that it can happen that quick.
As an added point I am on low carb now, well I think I am, it is under 130g a day anyway.