I have seen many different versions of what you are asking about. Depending on their disease process itself. a person may or may not have hallucinations which may cause them to see family that have already passed or even see animals, which seems strange to their love ones of course. And then there are those that as they near the end of their journey who start to see those who are waiting for them on the other side, which is sometimes what helps their passing be as peaceful as it can be.
The best thing to do in those situations is to tell them at that time that it is ok for them to go ahead and be with whoever it is they are talking about because most times they won't let go without some sort of approval that who ever they are leaving behind will be ok without them. Now granted we may very well struggle like crazy once they are gone but they isn't for them to carry with them that is for us to deal with, by working with our family and friends and support sysytems here for us.
Now to the other part of your question, I myself, have had several experinences with spirits being around me, either touching me, whispering to me or me seeing them. So I do not in NO WAY NO HOW NO SHAPE FORM believe that it the medication and WILL NEVER belief that!!!!