Hypoglycemic unawareness that occurs in diabetic patients when transfered from oral hypoglycemics to insulin, is due to-

Hypoglycemia unawareness-- loss of the warning adrenergic and cholinergic symptoms that previously allowed the patient to recognize developing hypoglycemia and therefore to abo the episode by ingesting carbohydrates. Autonomic neuropathy may reduce counter-regulatory hormone release (especially catecholamines), leading to an inability to sense hypoglycemia appropriately (hypoglycemia unawareness, thereby subjecting the patient to the risk of severe hypoglycemia and complicating effos to improve glycemic control. Reference : page 2426 Harrison's Principles of Internal Medicine 19th edition