I did not say that sundowning is an indication of dementia. I said that it is common to people with dementia as their brains fatigue later in the day at the same time as the sun sets.

Please do not try to read more into your situation than is evident. Nobody suggested a permanent diagnosis of anything.

Have you tried sleeping with music, especially soft lyrics ? The brain will focus on the understandable lyrics and may be able to ignore, even partially, your tinnitus. I find I do best with music and lyrics I know so my brain is not listening actively, more passively.