I have been to Japan twice for 9 months in total (originally from Germany). I didn't experience culture shock in Japan at all, but I also never really came back. Reverse culture shock can last for long. It is impossible to talk about this experience to anyone but those who have experienced Japan (or Asia) themselves for long time because most people can not even imagine how different cultures can be.
It well may be as far as social experience goes, you may not feel so much of "culture shock" in Japan as a foreigner, or at least easy on you. Generally Japanese people don't expect foreigner to act like them. You will never blend in, but flipside is you get perks for being foreigner there.
I don't know if this played any role in your experience but that seems to be what I have been hearing around me...
