Hello. As you mentioned that you were experiencing extremely LOW BLOOD SUGAR level . You were feeling heart beating very fast ( rapid ), sweating, with cold clammy extermities ( arms and legs ) , cold sweats . As you mentioned that there was not a correct reading over glucometer taken by your husband. Possibilities may be . 1 Glucometer was not able to detect any reading due to any fault as zero blood sugar level is not possible in human . Profuse sweating , cold clammy skin , cold sweats may be due to collapse ? In my opinion Hypoglycemia may be a reason of all these symptoms and reason may be . 1 Drugs insulin , sulfonylurea etc. 2 critical illness renal or cardiac failure, 3 endocrine deficiency 4 Non beta cell tumors like fibrosarcoma, hepatoma . However mere mentioning these symptoms are not able to evaluate any diagnosis , so complete history of illness is important . I would recommend you visit a physician and thereafter deal according to situation as this is an alarming condition. Good luck.