Q. A 72-year-old male was admitted two days ago for mental status changes. His wife reported on the day of admission the patient was “out of it” and did not respond to her questions appropriately. She also stated the patient has recently complained of intermittent bouts of abdominal pain, and decreased urine output, though she attributes these to him “just getting old”. There was no reported loss of consciousness or history or trauma associated with the event, and he has not experienced similar symptoms in the past. Although the episode resolved after approximately 15 minutes, she brought him to the emergency department for further evaluation and he was admitted for observation. An electrocardiogram (EKG) on the date of admission showed normal sinus rhythm and no acute changes. Cardiac enzymes were also obtained (x3) and remained within normal limits. Additionally, a head-CT (with and without contrast) was negative for signs of bleeding or ischemia, and no masses were detected. Yesterday morning, the patient was tachycardic and review of his labs revealed normal electrolytes with a slightly elevated blood urea nitrogen and creatinine clearance. You ordered IV fluids to be administered, which appeared to resolve his tachycardia. Overnight, staff report the patient had another self-limiting episode of altered mental status with no focal neurologic deficits. Today, his morning labs are still pending, though an electrocardiogram (EKG) was just completed (see image). Based on the information you have at this point, what is the most likely underlying cause of this patient’s altered mental status?