I have read where you do not reason, argue or correct your LO with dementia. It does seem to make things smoother when you just agree with them! My husband (of 50 years, newly diagnosed with dementia) calls me Mom and says he is my son on his confused days. I have also noticed that when I'm gone more than two or three hours out to lunch or on my volunteer job. He seems to get worse even though my 42 year old daughter is with him to answer any questions. This dementia is awful!
I am sure some - if not hundreds of readers here will find similar situations.
I believe your question is the 'why' - which may be unanswerable.
I believe the 'more confused' will / can change hour by hour, day by day.
It depends on the brain chemistry, degrees / levels of confusion, how advanced the dementia is. It seems like mercury - you just can't 'grab' it and know. This disease is more 'fluid' in that it can / does change.
Shocking to me, my client with severe dementia (spoke gibberish only) answered me one day when I said "I'm going to my car to get xxx". She said 'okay.' In my two years working w/her I believe she responded like this twice. Why? I do not think science / medical research knows.
I would ask you why you ask the question, and if you leave for 3-4 hours, how do you know they are more confused? (if you aren't there).
Are you feeling more sad figuring that is / gets more confused and asking for support for how you feel? (which may be implied in your question).
I believe there can be some momentary 'attachment' to a pleasant experience, i.e., your husband knows you are there (whoever he thinks you are) and feels 'good' / safe, etc. When you leave, those feellings of safety leave, too.
The question is, how long does a person 'remember' or feel that shift?
He could hallucinate and think that you were gone for days vs hours ... (time is generally moment-to-moment) or he could possibly think you left when you didn't (thinking you are someone else sitting there).
It could be the time of day when his energy shifts / lowers.
I encourage you to get the 36 Hour Day book. It is a good reference book.
And/or go on line and see what Teepa Snow has to offer (webinars, books, free clips, You Tubes). She helps people/family learn how to communicate with their loved ones inflicted with dementia. And, she explains how different parts of the brain work and how different parts of the brain function as it changes.
Gena / Touch Matters
And you are correct..."dementia is awful!!"
I wish you the very best as you travel this very difficult road with your husband.
Any changes do seem to cause confusion, even when they are just for a few hours.