What Causes Memory Loss?

My dad had a heart attack and a stroke. He is 80 and stubborn. He has stopped taking his medicine and refuses to take it. Since his stroke, his memory has completely vanished. He remembers some people, but 30 mins later couldn't tell you who they are. On top of that he has been seeing people that are not there. Today his memory is completely gone. He was petting the surge protector because he thinks it is a dog and has started seeing a lot more people that is not there, both inside and outside the house. What can we do? Should we get him to the ER?