I have had some personal experiences but it does depend on that person, but I will tell you my personal experience.
When I was 6 years old, I have always told my grandfather bedtime stories before heading off to bed myself, so one night as I finished reading "Snow white and the seven dwarves" I kissed him good night and went off to my room, as usual I went to bed and woke up the next morning. As I started to wake up my mother was sat beside my bed (which was unusual for her since she didn't live at the house at the time)
I hopped downstairs and saw my grandfather in his chair looking down at the floor, I approached him and asked him what was wrong, he replied
"I am so sorry, I love you"
"I love you too grandpa please don't be sad"
I smiled at him and he smiled back at me, I headed into the kitchen to make some cereal, as I was doing so my mother approached me and asked
"Hey honey, who are you talking to?"
"Oh, grandpa, he's really sad for some reason, he said he's sorry, do you know why?"
My mother looked at me and went white in the face, she then continued to add, in a quivering voice
"Oh, you couldn't have honey, he passed away last night, he had a heart attack"
I was confused, how could he have died when I was just talking to him? So I went to show her but he wasn't there.
Still to this day I believe that my grandfather didn't want to pass away, it wasn't his fault, and I still believe that he is with us. But it all depends on the person whether it be physically seeing a ghost/spirit or hearing one or being pushed when there is no one around, but I guess we will all know one day.