So, I thought I'd post my recent experience.
(tl;dr if you think you have something, get checked. This place is good
http://www.yoboukai-shinjukusatellite.jp/sp/clinic/)
About a month and a half ago I was with my FB (mid-40's, married salary woman) and after going down on me, she hopped up and climbed on. After about 20-30 seconds and coming to my senses, I got her off and grabbed a condom. I didn't think much of it at the time, as after 2 weeks or so there were no major symptoms. In the past, I've had both gonorrhea and chlamydia and both presented the same---not a case of "Gee willikers, I wonder if I have an STI?" and more "Holy fuck, my cock is on fire when I piss, and what the fuck is this white shit oozing out? I best get this STI sorted asap."
So, I'd been having a bit of odd feeling around my balls and the bladder area---a bit of burning after peeing at times. Of course, Google assured me it was the "silent STI" chlamydia, so I started getting paranoid. Thought to ride out the paranoia, but once that demon gets in it's hard to expel. So, finally bit the bullet and decided to get tested. Came to TAG for some advice---hat tip to User#8628 and MikeH for the info about Shinjuku Satellite Clinic. Painless, easy in and out experience. Dropped in, got checked, results on their site in 2 days. Negative as I'd thought. After talking to regular doctor, seems it was prostaitis brought on my advancing age and spending 15+ hours on the bike every week.
Anyway, if you have any inkling you have picked up something, I highly recommend this clinic to assay your fears.
http://www.yoboukai-shinjukusatellite.jp/sp/clinic/
PS---there was a gaggle of very attractive young ladies there the same time, so I'm guessing it's a popular place for working girls to get checked.