Very Low Blood Glucose

I can tell you what it means from a diabetic angle. Very low BG means insulin is too high. Your body needs sugars to function and without enough coma and death could occur. For diabetics this low BG means they need to eat sugar ASAP and give less insulin, change their diet, expend less energy - to balance their BG levels.

I imagine many people can have low BG and not be insulin dependent. Usually I think this is called hypoglycemia. You can find more info here:

http://diabetes.niddk.nih.gov/dm/pubs/hypoglycemia/

and a little more here:
http://www.emedicinehealth.com/low_blood_sugar_hypoglycemia/article_em.htm