The term "spontaneous hypoglycemia" was coined by the physician Seale Harris.
It is a vague term that is currently considered to be too imprecise to be useful by doctors interested in hypoglycemia, though it may have historical value.
History
When Seale Harris was writing about hypoglycemia, the only two kinds that were well understood were diabetic hypoglycemia and hypoglycemia resulting from insulinoma. He asserted that there were likely other types as well. His assertion was widely enough accepted that the diagnosis was assigned to, or claimed by, a large number of patients with otherwise unexplained adrenergic symptoms.
His contemporary, a surgeon named Allen Oldfather Whipple, formulated the Whipple criteria as a sieve to sort out those who might have an insulinoma requiring surgery from those with symptoms but not measured low blood glucose. They are still in use for exactly that purpose.