That’s interesting to hear about Japanese healthcare. Given the level of development and health data, I had assumed they had a pretty first rate system. Other places in Asia at similar development (HK, Singapore) blow away US healthcare in my limited experience and opinion.
My culture shock hit around the 6 month mark for what it’s worth, but I spoke hardly any local language and I was slow to even try. You have a serious leg up having been there and probably speaking some of the language. My guess is the worst that will happen is some mild annoyance that you can’t find something. As an example, Netflix. Step back in time and find some video media. Or maybe find a local theater that either has movies in English or dubbed for the same. Use that as a chance to get out more. Things speed way up once you have a friend locally, be they an expat or a local, but obviously much better having a local friend.
You will eat differently, live differently, travel differently, etc. Give yourself time to get adjusted to all that new routine.
Bear in mind I have zero experience with the US healthcare world. But on your remark, it may be a generational thing: very young doctors (around 30s) generally felt much more competent to me than their elders (from 40s up to 80s).
I have been witness to two misdiagnosis, one life threatening, in my last couple of years there, both from doctors in their middle-late 40s, so I am probably very biased.
Also, in my limited experience relying on them only a couple of times over the course of 10 years, the paramedics (exclusively in ambulances) were amazing. Sadly, they may have to discharge you in a (shiver) clinic.