I cared for my Mum with dementia for 10 years. The episodes of the early stages I only recognized in hindsight. Stressful or unfamiliar situations were remembered differently to how I saw them at the time. Towards the end she argued about which medication to take, etc. But was docile at the doctor's surgery. My Mum also developed macular degeneration and couldn't read and watched very large screen TV up close.

I concur with @Smeevy, especially about not arguing / correcting.

All I can add is to grow a thick skin, because you will be attacked over hallucinated events and to accept that the condition does go through swings. There are times when they seem almost like old times and then without warning out comes something totally hallucinatory.

It's like they are wearing Adam Savage's (MythBusters) T-shirt: "I reject your reality and substitute my own." And you just have to go with it.