Yup, definitely sounds like "hostess mode" to me too. People with dementia can suppress the symptoms of dementia when faced with family members that they dont see often, medical staff and other authority figures, but it takes a lot of effort, they cant maintain it for long and it leaves them exhausted afterwards.
Its really irritating as the person they are seeing then thinks that you are exaggerating, they are really not too bad after all and then you are left to pick up the pieces with a tired grumpy person with dementia.
Wanting to be with you all the time sounds like Shadowing. People with dementia often get to the stage of being frightened when left on their own - even if their carer is only in the room next door - as they need someone with them to reassure and direct them, so they want someone within eye shot every waking moment. Also, everything becomes about them. They have to be the centre of every conversation and every meeting. They want to direct every conversation and, if they are not, they are convinced that people are talking about them. Mum used to be convinced that complete strangers who were just having a conversation nearby were talking about her! Im afraid that the only way to get a break is to find someone to sit with her.