It definitely sounds like low blood sugar to me...
I got this in my last pg - and the feeling is awful isn't it... luckily I never got to the point of fainting though.
I have had it once so far with this pg, and it hit me really hard and quickly, and took me a couple of hours to recover...
It can happen to anyone, whether pg or not, or whether a diabetic or not.

Make sure you eat small meals frequently, and always carry a spare snack or two with you (maybe something like dried fruit?) in case you aren't able to eat for a while.