Sometimes when people are talking to me, I often respond with some of my characters’ catchphrases. Other times, I catch myself adopting some of the same mannerisms my characters have. Or maybe I’ll see a person and think that he or she looks like one of my characters.
I would say that events like that are not insanity; they are a kind of subconscious part of the writing process. It’s been proven that when you get fed up with something, be it a certain part of something you’re writing or a math problem or relationship issue, that when you “sleep on it,” or walk away from it for awhile, your subconscious mind will try to sort it out.
Maybe by seeing your characters in yourself and in other people, your brain is continuing to work on your story while you’re not actually sitting at the computer typing. That way when you do start physically writing, you’ll have more ideas and you’ll be able to work your way out of tight corners.
So it’s good to let your ideas rest for a while. Even if you don’t literally “sleep on it,” some time away can do you quite a bit of good!