Glad dad is on the road to recovery.
As for the hallucinations, my John had them with morphine too and now won't touch it. Brain fog was also normal for him. Johns was following major surgery but not PC, however, it is still very early days for your dad and you also have the consultant saying it's a post op issue.
IF dad could just accept that he will be like it for a while perhaps it will make it easier for him.
I hope others come along with their experience of how long it lasted but remember we are all different and some may never have had the problems that your dad and my husband did with the drugs.