As a paranormal investigator, this is the very most asked question I have gotten over the years and I have developed a special technique to help people figure out if they encountered a ghost or not.
In my book "Was That a Ghost?" $2.99 on Kindle and Nook, I explain types of paranormal encounters, the "Trinity of Relevance" to discern if you had a ghostly encounter, give quizzes and real life examples, as well as help people to know what to do next after they realize they've encountered the other side.