I'm guessing you're thinking of driving over here and not Japan, now that would be scary.
For me, driving on the wrong side of the road doesn't take long to get used to in the States because the roads are so logically laid out. Here in the U.K. things can be tighter and more tricky to navigate, you are often giving way to traffic at crossroads instead of having your own signal so you have to think more about that. If you can practise going round a roundabout in your head too that'll help a lot as you'll encounter many of them here, I thought they didn't exist in your fine nation until I drove through Clearwater! An auto is a no brainer unless you've driven manual/stick shift all your life.
I've yet to take my car across to mainland Europe, for some reason I think it would be the most difficult as you're driving on the wrong side of the road (or the correct side for most of you) yet the steering wheel is kerbside, that could fool me if tired.
Generally I'd say don't worry about driving here but try to stick out of the big cities during the week, unlike the states we built our cities with only horse and cart in mind and now we are paying the price, this country couldn't make it harder to own a car and just drive normally through major cities like you can over there.
All the best with your future wrong side driving!