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.