Which endocrine condition would you suspect here?

Medical Case Details:

An 81-year-old male had experienced vomiting, dizziness, and appetite loss for two weeks. There had not been recognition of diabetes before the onset of this illness. On admission, he showed impaired consciousness (Glasgow Coma Scale score, 12) with no neurologically abnormal findings or abdominal tenderness.

However, he had a dry tongue and decreased skin turgor. His height was 158 cm, body weight 42.1 kg, and body mass index 16.7 kg/m2. His blood pressure was 138/78 mm Hg with an irregular pulse and heartbeat. His body temperature was 35.8 C. Electrocardiography revealed atrial fibrillation. He had no familial history of diabetes. There was no history of falling or bruising.

Question: Which endocrine condition would you suspect here?