From your question , I believe that there was no previous history of such behavioural changes .
Hence have you checked the Electolytes level Potassium (k) & Sodium (Na) in blood .
Most psychiatrists forget this basic step.
It is usual that Old age people , who may be consuming medicines for High Blodd Pressure
may have depleted thier Sodium levels which could , make Mental confusion, and such behavioural changes.
Usually eating more salt and maintaing NA level to 135 , is all that is required.
Hope this helps.
Psychiatry is the medical specialty devoted to the diagnosis, prevention and treatment of mental disorders. These include various maladaptations related to mood, behaviour, cognition, and perceptions.