A 72-year-old man with a 3-year history of progressive memory loss and difficulty with word-finding is brought to the hospital by his son. Over the past 2 days, he has become acutely confused, agitated, and disoriented to time and place. He is pulling at his IV lines and does not recognize his son. On examination, temperature is 38.5°C, heart rate 110/min, blood pressure 145/90 mmHg. Urinalysis shows pyuria and bacteriuria. Cognitive testing shows marked fluctuation in attention and awareness. Which of the following best describes the acute change in his mental status?