The buddy with whom I learned diving used to panick on each first dive of a trip. According to our OW instructor, it happens. Breathing underwater is not a natural state for a human being and goes against aeons of evolution. So panick is an normal response and happens in some people. Mind you, I'm not sure at which point this is true or was said just to make her feel better, but sounds good enough for me.
It used to happen only on the first descent. After that, she would usually be a bit nervous for the first day of diving, and then absolutely enjoy the rest of the diving. With more experience, and taking it slowly, now she got past the full blown panic and is just nervous on the first dive. The rest of our trips are great.
We tried to solve the issue by always going extra slow for the first dive, being attentive, and of course, warning the divemaster so that he can react quickly if needed. Also, I have been trying to take her on longer dive trips, where we would have several days of diving, so that she can really have time to enjoy the diving, and not always go from "first dive in a while" to "first dive in a while", with all the anxiety that brings.
For me, your situation looks a bit the same, except that you have been diving already before without this and it started only recently. I'm not a psychologist, but if I go with the explanation our OW instructor gave us, maybe some latent ancestral fear manifested itself during this dive? Maybe it has been extra long since your last dive? Or maybe it's something else, with another triggering factor?
Anyways, based on our experience, what worked for my buddy was to go extra slow, be well surrounded, and dive (preferentiably in a familiar and "safe" environment). Maybe try going for longer dive trips, more than just a few fun dive, so that you have time to remember how enjoyable diving is past the initial anxiousness?
Additionnally, my buddy and I are currently doing our Rescue course, in order to learn better how to deal with this type of situation if it arrises again, but I see that you are already rescue certified. Maybe a refresher of some kind might help?