A steadier ground guide to the hospital stay, where new confusion in the first days is common and usually treatable, and where the person who knows him is the most useful instrument on the ward. What may be happening, what to say to him and to the staff, and when "worse" means something that needs a nurse now.
Notice the urge to apologize for him, or to explain him, every time a new person walks into the room. The confusion you are watching is frightening, and it is yours to feel, and one breath before the next nurse arrives keeps your voice the steady thing in a room that has none.
Before anything else: a person with dementia who becomes newly confused in hospital is often in delirium, which is a medical change layered on top of the dementia rather than the dementia moving faster. Pain, an infection, dehydration, constipation, a bladder that will not empty, a new medicine, and glasses or hearing aids left in a drawer at home are the ordinary causes, and most of them are treatable once someone hears that this is new.
You cannot treat the infection or rewrite the medication list, and you can change most of what the room is doing to him.
Write down the hour he is clearest and the hour he is worst, what he ate and drank, when he last passed urine, and how he slept, dated. The ward records vital signs; nobody records that he was himself at ten and gone by four, and that pattern is what makes delirium visible to the next doctor who rounds. If a new medicine was added, note the day, since the confusion that follows it is the most reversible kind.
Print the emergency room handoff and the one-page log: the handoff for the front desk, the log for the ward.
This is what the tracking is for. On a ward the clinician is the nurse at the bedside, and the hour it started and the hour it changed are what turn "he seems worse" into a page to the doctor.
The ward measures him against his chart, and you measure him against Tuesday. Yours is the measurement that catches this, and it does not need a medical word to be true. Sitting in the chair by the bed without answers is most of the job.