Low C-peptide, low proinsulin, high plasma free insulin and low glucose, in a nurse, who presents with episodes of symptoms of hypoglycemia without apparent precipitants, is straight out of FA's textbook definition of a factitious disorder. See FA 2019 p554
c peptide = endogenous insulin , low c peptide + low blood glucose = exogenous insulin. very simple
In the pancreas' beta cells, proinsulin splits apart to form one molecule of C-peptide and one molecule of insulin.
C-peptide testing can be used to help evaluate the production of insulin made by the body (endogenous) and to help differentiate it from insulin that is not produced by the body but is taken exogenously and so does not generate C-peptide.