Most of the time, culture shock happens when you arrive in - or leave - a country.
Japan shocks people. Even if you've lived in a city all your life, Japan throws you.
And that's from a country that more or less invented Paris Syndrome. Japanese people are confused by Paris. The rest of the world is confused by Japan.
Moving from one part of Japan to another can create the same feeling.
Let's say you arrived here as an English teacher, assigned to a little school in a village. After a couple of years, you want to move on. You take a job in a city - whichever happens to be nearest. And when you get there, it's bewildering.
Suddenly, the signs written in Japanese that you've worked hard on understanding are illegible. There are just too many, and your brain's given up. You used to happily walk everywhere, and now you fight for space in train carriages and on bus gangways.
I've spent the last 6 months in Kansai. Osaka's a decently-sized city, but it benefits from being very walkable in the centre. Nice and flat. Also good for the cyclists - if they stay on the road like they're meant to and don't invade the pavements.
The west side of Japan has a reputation for being more chilled and casual. It's easy-going. People from Osaka often ask me why the hell I'd ever want to visit/live anywhere else.
I can't say I've been fully converted to the Kansai side. There's a lot of Japan I'd still like to see - Okinawa, Hakata, Hiroshima, etc. I can, however, see why they'd ask.
All of my previous Japan trips were to Tokyo. I felt like I was used to it. And I love wandering around Tokyo, because you can't go more than 10 steps without seeing something interesting. Living in London at the time also helped immensely. Squeezing my way onto a packed train or through a crowded shopping centre was no big deal.
Osaka has changed Tokyo for me. Irreparably. Not to the point I hate the place - far from it. I will always love Tokyo. But it's fair to say my perspective on both cities has changed.
I spent 4 days in Shibuya over the summer, and it felt like claustrophobia. I've lost my tolerance for large crowds somewhere along the way.
And they have just as little tolerance for me. Osakans tend to give my luggage a wide berth. They can afford to, the trains are rarely that crowded. At times, it feels like fellow travellers in Tokyo want to take a shortcut over the top of my suitcase. I got pushed out of a train carriage today. That hasn't happened for a very long time...
At least Pokemon GO has given me a cover story for frequently looking at my phone. No, I'm not lost, I'm trying to catch a Pidgey. I've spent most of the summer ambling around slowly and taking everything in. Try that around any station on the Yamanote line and you'll get run over. I keep forgetting to keep pace with the much larger crowds in Tokyo.
Sure, I'll eventually get back to being used to Tokyo life. If I managed it before then I must be able to again. It feels harder a second time, though.
How are you supposed to readjust when you haven't even left the country?