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Thanks all for your kind posts.
He is definitely not well as I have cooked a chicken and he would normally torture me for a piece - no, not tonight.
Also, when I was talking to him this afternoon I was calling his name, he was looking a different way from where I was sitting and when I say "get away from my window" - he is usually over barking at the window.
He has been like this before so I am not too despondent. Will make an appointment on Monday.