Ghostly visitations fall into several distinct categories. Here are a few of the most common. Typically, the ghosts appear only once to a special loved one who may be many miles away at the time of the accident.
Doppelgangers are ghostly doubles of living people.
Often the doppelganger is not visible to the person himself, and will simply follow the person around. In some cases a person will come upon his own doppelganger who is typically engaged in some future activity. Doppelgangers are traditionally considered omens of bad luck or even death. Many apparitions are always viewed repeating the same motions or scenes. Many classic hauntings fall into this category.