Sex makes me feel claustrophobic...

I have been with my partner for over a year now. As we do not live together, we tend to have sex every time we see each other which is usually once or twice a week. I never really used to, but I have come to the conclusion that I struggle with physical contact. As horrible as it sounds, having sex makes my skin crawl and I feel so claustrophobic and it’s generally not a very enjoyable experience. It’s not because of the way my bf makes me feel, and when I want to stop he is fine and we just cuddle. I don’t know what it is that makes me feel like this and I feel bad because I want both of us to enjoy the experience. I don’t know how to bring it up without it sounding offensive. Any advice?