I know I'm being stupid.
A few weeks ago, I went to use a public toilet and noticed there was a smudge of something on the seat. I wiped it vigorously off (I'm pretty OCD like that) and it looked dried in, so there was still a tiny smudge left, but I was desperate and there were no other cubicles available so I went to the toilet.
Now, I'm scared I may have transmitted HIV from it. I know I had a test on Monday that proves I'm HIV negative, and everything I've read has said transmission like this is impossible....but my anxiety has kicked up, and won't let me stop thinking about it.