I am a strong believer in spirits.
I strongly believe that if you experience "a door closing" it could be that the walls/floors are not leveled, maybe a hinge is missing or the door doesn't latch tightly/correctly. Maybe the the window was left open across the room..the point is to check your home.
I strongly believe that if a "book fell off a bookshelf" was it not placed back correctly? Was the book stacked high on top of other books and when grandma came in the front door you did not hear her come in the house and your book fell off the bookshelf because of vibrations? It is possible.
What I am trying to say is that a lot of people believe that somethings like these are paranormal. It's our responsibility to investigate and find out why this happened. There can be many explainable reasons why "something" happened. We cannot assume it's a spirit/ghost etc. Just watch "Ghost Hunters."
For me, I have checked out why something happened. Yes, I was scared but I had to go check. If you've never experienced anything paranormal you will not understand until it happens to you. Since I work at a hospital for many years and have had a lot of things happen to me growing up and working in this environment. I've known people that started as a housekeeper and never believed in ghosts/spirits. I just laugh because it doesn't take long for them to bring it up again and they usually have a story to tell and all the housekeepers say: "I told you so."
Something to think about.