A 50-year-old obese woman has long-standing type 2 diabetes mellitus inadequately controlled on metformin and pioglitazone. Insulin glargine (15 units subcutaneously at bedtime) has recently been started because of a hemoglobin A1C level of 8.4. Over the weekend, she develops nausea, vomiting, and diarrhea after exposure to family members with a similar illness. Afraid of hypoglycemia, the patient omits the insulin for 3 nights. Over the next 24 hours, she develops lethargy and is brought to the emergency room. On examination, she is afebrile and unresponsive to verbal command. Blood pressure is 84/52. Skin turgor is poor and mucous membranes dry. Neurological examination is nonfocal; she does not have neck rigidity.Laboratory results are as follows:Na: 126 mEq/LK: 4.0 mEq/LCl: 95 mEq/LHCO3: 22 mEq/LGlucose: 1100 mg/dLBUN: 84 mg/dLCreatinine: 3.0 mg/dLWhich of the following is the most likely cause of this patient's coma?