While I've only had the experience of going back for another year after a fairly short stay, I would simply recommend to not create any expectations that are too big in your mind. There will be of course readjusting, and images in your mind about the time you had over your years in Japan of course will warp and you'll remember the good only. (which is not really a bad thing either)
I'd say just give yourself some time and don't expect things to instantly be as magical within the first few months as the years that you have been there in the past.
Then again though, just a comment.