Nightmare of a dead person?

I had a relative who died some 30 years ago. I was a kid back then and was at the funeral. He died of an ordinary heart attack and nothing special about the funeral. But over the years and up to the present I have recurring nightmares about his coffin being dug up and opened years later, or finding out his coffin is actually buried in the back yard of my house and other ghastly dreams. I never dream he comes to life, only gross displays of his body. I probably shouldn't have to ask why I dream this, but I'll ask anyways.