"How to keep going?" Dam good question. Some good feedback in this thread.
I've not had an experience like you. But I have been plenty scared at times. I deal with how to boat and what edge I want to dance constantly. I'm an older boater now and not trying to "get better". I typically paddle stuff a class or even 2 classes easier than I'm capable of. I want to be styling as much and often as possible. My margin for error is a lot less than 15 years ago. I would agree that paddling some easy water would be a good start. But also would suggest that pushing back to harder water does not have to be a goal. Just getting on a beautiful rio with good friends is as good as hitting a hard line.
I also find that for most of us a big part of boating is adventuring. And adventuring can happen on easy water. Desert floats, self support in slot canyons, sea kayaking the coast, a class 2/3 wilderness run, these all hold the essence that we crave.
Back off, give yourself time. Enjoy the rio without the adrenaline for a while.