Panic attacks during sex

Alright guys so my bf and I were doing it in the shower and all of a sudden he says "I think I need to go sit down, I'm having trouble standing and I feel like I might faint." So I take him back to the bed and have him lay down. Then he says he can't feel his hands or feet. I check his pulse and it's racing like crazy. I'm really worried cause this has happened before, and he just has to lay there for hours until he feels normal. He said he had his first panic attack when he got his first bj from some girl in hs and she used a lot of teeth. But with me, he doesn't feel scared or bad or anything. He just randomly gets overwhelmed and we can't figure out why. It sucks cause he kept apologizing for feeling sick, and I kept telling him it was okay, that I just want him to feel better, but sometimes I don't feel like it's okay. It's almost every time we have sex now he has to stop before either of us finishes to slow his heart rate so he doesn't have an attack. I'm not mad at him but I just have no idea what's going on and I want him to feel better so we can get back to enjoying ourselves - him not being upset that he's feeling sick, and me not worrying that I'm making anything worse.