Morphine side effects

My father just had a surgery for his aorta.  The surgery was sucessful but a few days after the surgery, he developped water around his left lung.  When that was diagnostic, the surgeon decided to put a drain to drain out the water.

It was so painful after the installation of the drain that they have to inject morphine to manage his pain.  The dosage is 7.5 mg and he had 5 shots in the space of 2 days.  

On the 3rd day, they stop the morphine and he seems to be hallucinating, lots of confusion, and he had a memory lost - all events from about a month ago -  how long morphine will last in the system?  Is this mental issue a long lasting problem?

Please help.

A very worried daughter.