Whenever I am deep into reading a book—invested in the characters and the outcome of their stories—I start to take on a few of their traits. If the main character is southern and the writer has written some of the dialogue in a bit of a southern twang, I want to start talking like that. When there is a character I really connect with, that uses certain sayings or has specific mannerisms, I start to use those and take on those physical mannerisms. It's usually only for a short amount of time. It's similar to when you are talking to someone at a party and you start to mimic their body language. I think this is mostly unconscious.
I just went to Google, and this behavior is called "mirroring" and "mimicry". We do it subconsciously in an effort to increase rapport, to make someone like you more. These nonverbal communications can include taking on someone's accent, copying their posture, or even using the same words they do.
Now that I know this, it doesn't seem so odd that I would do these things while reading, because when I read, the characters become real to me for a time. While having a conversation with someone, I have been known to bring up something funny a character did in my book, as though it happened in real life and we are friends.
I get deeply invested, as you can see. So invested, in fact, that with the current book I am reading, I am starting to become a bit of a hypochondriac. The book is a memoir, and the author was diagnosed with breast cancer. I just had my annual mammogram and have not yet received my results. So naturally, I am now convinced that I also have breast cancer. I imagine this every time I go in for a mammogram, especially after my first ended in a biopsy. But now, as I am reading this book, it seems as though, if I did have cancer, I would have someone (through a book) who was going through the same thing, someone who would understand and empathize. At least this is an actual person, not a fictional character.
Do you ever get this invested in a book character, or a movie or TV character?
UPDATE: My mammogram was clear, and now I am reading a book about someone whose husband is leading a secret second life as a con man and is mixed up with some very bad people. Let's hope I don't start suspecting this of my spouse. (I do have a good pair of spying binoculars though, if I do need to look into his secret life.)