It's when you don't have any glucose in your bloodstream and your blood sugar is low. A way to prevent this, drink sugary drinks and eat a lot of protein. it's almost associated with diabetes, but the exact opposite. If you want to description from somebody who has this, you would be dizzy, you can't pay attention to anything, you're shaking too and everything you see is white until you fall on the floor and possibly have a seizure.
