Hi thank you all for replies. Although i forgot to look at my original post till today!! Perhaps it's not just Rosie who's losing her marbles

I took her to vet for a check up , just in case , but he couldn't find anything wrong with her.
She's still getting what i'd call panicked when in the kitchen at night. Don't think there's anything in the garden ( not that she usually notices even when she's out there with birds / cats etc ) as if she heard something she'd be scratching at the back door. And her behaviour starts just a couple of minutes after we leave her.
I've also noticed that she is pacing around more during the daytime. I think it's worrying me more because it seems to have happened all of a sudden , with no build up to it. But perhaps like someone said , I just haven't noticed all the little changes beforehand.
We have now been leaving her the whole of downstairs at night time which has stopped the stressed behaviour , although can still occasionally hear her plodding about. So I dont fully understand that if she's doing it to be with us , why is she happy in another room , without us?
Many thanks to all for your help and suggestions