Of course it's "possible" that your piercer "ACCIDENTALLY," and "unintentionally" reused a needle. Anything is possible. Just as some things are extremely unlikely, and this is one such example. If this person came highly recommended to you and is, as you say, a "professional," then I seriously doubt you have anything to worry about. Tattoo and piercing businesses are under a lot of scrutiny by the Dept. of Health. They would not be in business long if they weren't taking every precaution for the publics safety. These people make their living with their "art" and they aren't stupid nor are they evil.
You can go talk with the person who did your pierceing and tell them you are nervous about HIV. That may help calm you down, but I doubt it. Your HIV anxiety will simply convince you the person is lying.
At 12 weeks you can go get tested for HIV which will give you a totally conclusive result. You could then relax.........until the next time you fear you let your guard down/
You can get yourself educated about HIV, which I strongly recommend.
And most importantly, you can get into some therapy for your HIV anxiety.
Just do SOMETHING that will help you get a grip on your irrational fears.
Find and deal with the cause of your anxiety........it will set you free.
Peace
Greenlydia