From your description it appears that your father in law has Delirium. It is an
acute confusional state that needs urgent medical attention. Several factors can cause and precipitate Delirium. Pre-existing
cognitive impairment (such as short term
memory loss) makes a person more vulnerable to delirium.
In old age, Delirium is usually due to multiple causes. Your father in law too seems to have multiple factors: earlier cognitive impairment,
dehydration, fever, diarrohea, morphine etc.
In my practice I give instructions about environmental management which are helpful.
You should not oppose him.
Be gentle with him. Avoid physical restraints.
Keep him in familiar surrounding and with familiar people around.
Give him gentle orienting clues about time, place and person.
Keep the lights bright in day time and dim at night time. Keep noise minimum at night.
Keep him awake and engaged in day time.
Ensure that he takes enough liquids. Try to give fluids with adequate electrolytes. Oral rehydration solution (ORS) is good.
The doctors may order blood tests to see if there is
electrolyte imbalance etc.
If morphine is the main cause for delirium, it should recover as morphine is cleared away from body.
Once he recovers, take him to a
psychiatrist or a
neurologist for evaluation for dementia in view of his short term memory loss.
Hope this answers your question.