there is no definite numbers. it simply means low blood glucose level or relatively low.
in hypolycemia unawareness, its vital to treat them early because they go into coma faster!
what leads to hypoglycemia?
low levels of counterregulatory hormones
low source of glucose
renal impariment leads of hindered degradation of insulin hence decreasing requirements of insulin intake in diabetic patient! ( esp since they may have DM Nephropathy)
females. have overactive parasympathetic flow hence they are more liable to early postprandial hypoglycemia.