I had a condom break just once (surprise, it was also in Osaka) and went through the normal phases of panic and paranoia. Main thing to keep in mind is it's extremely difficult to contract HIV through vaginal sex. After returning stateside and waiting the recommended time period, I went to the clinic, explained what happened and requested a full battery of tests. They asked me about my lifestyle--do I give/receive anal sex, do I engage in anal sex with men, do I use intravenous drugs/needles? I answered no to all, and they told me that the chances of me contracting HIV were so incredibly small that they would not perform the HIV-specific blood test unless I either tested positive for another STI or began engaging in other specific risky sexual behavior. I asked, "So can I change my answer and claim to take it up the ass and you perform the test?" and the nurse didn't think it was funny.
What you DO have a pretty good chance of contracting from a condom break, assuming the partner is infected, is a host of other nasty but curable STIs, like gonorrhea and chlamydia, and if you've got those you'll know it soon enough. A buddy of mine has caught the clap two or three times during marathons in the P.I., and those were from receiving a BBBJ from a bar girl.
Just wait the recommended time and get tested and in the meantime, difficult as it might be, just try to relax. The chances of you catching something really dangerous are very, very small, and what you're more likely to catch, if anything, will in the end be a really funny story to share on TAG.