We didn't use a condom...

I had unprotected anal sex last night. Please save the judgement I know it was dumb. I never usually do that but unfortunately last night went a long with it. Anyway, I was the top. I'm now worried that I may have contracted HIV and it's freaking me out. I've conflicting advice on the internet and just wondered if my chances of exposure were significant enough for me to take PEP. Any advice welcome, please no judgement.