Mrs Daniels is 75 years old and is known to have Ischaemic heart disease and severe knee osteoarthritis. Drug history includes Co-codamol, Aspirin and Atorvastatin. Her daughter asks for a GP home visit as she is concerned her mother has become progressively confused and drowsy over the last 2 weeks. She is not aware of any cough, diarrhoea, vomiting or urinary symptoms. Her neighbour was also concerned that her personality was different and recalls she had a minor bump to her head falling on the garden patio 3 weeks ago, but got up unaided and had no concerning injuries.
Based on the history alone, what is the most likely diagnosis?