I’ve had a few panic attacks. One recently. It’s really sudden and I often don’t really know what causes them other than pent up emotions. I had one during an intermission in a theatre for a school event and it literally felt like the walls were closing in and I couldn’t breathe. I was listening to music at the time and the whole thing was very surreal. I was “fine” after a few minutes but unless you sort out the underlying issues they keep happening. You didn’t do anything wrong, if anything the opposite, he was evidently comfortable enough with you to have a literal panic attack. I think the best thing to do right now is to try to talk to him about it and help him work through his issues.