Complex sentence: The Queen Mother had been suffering from a persistent cold which she caught during Christmas 2001, being bedridden at Sandringham after making her final public engagement on 22 November 2001, when she attended the recommissioning of HMS Ark Royal.
Split into simpler sentences: The Queen Mother had been suffering from a persistent cold which she caught during Christmas 2001. She was bedridden at Sandringham after her final public engagement on 22 November 2001, when she attended the recommissioning of HMS Ark Royal.