Panic attack.

So while I was having sex with my boyfriend, I started to feel like i couldn't breathe. I hurried up and told him to stop and as soon as he did I started bawling. I don't know why. This wasn't a full blown panic attack, but I couldn't breathe or talk to move. All I could do was lay there and hyperventilate and sob. I have had panic attacks before, some for a reason and others for no reason at all, but I never had one during sex. Has this happened to anyone else or anyone have an explanintion?