So...not really much to explain her so it can be before or after the person turns into a ghost.

Senario 1:You were about to go to bed till you herad a voice said"Hello!".You turn around but didn't see nothing,so you shurg and sit on a bed thinking about the voice till the voice go louder and reveal a ghost right in front of you"Boo!"the ghost yelled you...

Scenario 2: Make up your own.