Im talking with fake accents and im not purposely trying too?

I've been in situations where people have started talking to eachother with fake new york accents and london or australian accents and I've started to notice its directed towards me. I was at a party and a group of people started talking to eachother with fake british accents and I thought it was weird but ignored it. I went outside and started talking to this girl and she answered me with a fake british accent and I knew it was directed towards me because she was talking to other people with her normal american accent. So they were basically making fun of me. There's been other situations similar to this and I realize I'm talking with fake accents but I'm not doing them on purpose which makes. Me feel worried to speak up. I'm naturally quite and worried to speak up half the time and this makes it even worse. I'm from texas and I've never been to new york london ausralia or boston so there's no reason for me to talk like this. I've witnessed this asian girl do a similar thing when she gets drunk she was talking with a new york accent and I viewd it as bizare so I could see how someone would view me as fake. I'm not a fake person and I'm not realizing I'm doing it. Bottom line knowing now that it wasn't all in my head and that I'm really talking like this I just want to know WHY? I can't answer this question. What could be the reason for this? I need to get over this fear of thinking I'm gonna give off a fake accent everytime I open my mouth. And this isn't always happening but it does happen sometimes and the fact that it is is ridiculous.