I think I was a prostitute last night

So last night was like any other night out with the girls, dinner, drinks etc. we met some guys, went to the club with them, drank a little more then at the end of the night I ended up going back to my room with one of them. Super attractive guy, we got along and everything was great, even the sex was amazing but when I woke up this morning he was gone and there was an envelope of cash sitting on the bedside table with $500... You can imagine how confused I am by all this. I didn't do or say anything to give him the impression that I was a whore. I don't even usually sleep with guys on the first night but this kinda just happened and now I'm sitting here trying to piece it all together.