Do people really see ghosts of people who have passed away?

People claim to have seen loved ones that have died and have even spoke to them, Eccl. 9: 5-6, 5."For the living know that they shall die: but the dead know not any thing, neither have they any more reward; for the memory of them is forgotten. 6. Also their love and their hatred, and their envy, is now perished; neither have they a portion for ever in any thing that is done under the sun." tells us that this is not true.I think that sometimes people miss their loved ones so much that they can make themselves believe that they are seeing something that is not there.I have a good friend that lost her son last Christmas eve and she truly believes that every time she sees a butterfly, that it is her son letting her know that he is okay because she saw butterflies land on his casket as they were burying him.We all mourn in different ways but we can not lose sight of whats real and what is not.May peace be with you.