A complication of diabetes mellitus that results from extremely high glucose (blood sugar) levels without the presence of ketones, a by-product of fat metabolism; abbreviated as HHNS. Sometimes wrongly called diabetic coma, HHNS is characterized by decreased consciousness, extreme dehydration, and very high blood glucose levels (often over 600 mg/dL). Symptoms may include increased thirst, increased urination, nausea, lethargy, confusion, and seizures. HHNS is usually seen in people who have not yet been diagnosed with diabetes or those who have neglected their diabetes.