(A week after the synagogue attack, I wrote the following privately and later decided I could share it.)

Something happened during Shabbat services yesterday, and I'm not sure whether I should be trying to suppress it or letting it run its course or what.

The surrounding community has been really supportive and there was a (national?) drive to "show up for Shabbat" to show bigots that they can't intimidate us. So I knew to expect a larger turnout than usual. Our morning minyan usually has about 30 people, fitting comfortably in our chapel; yesterday we had 200 and had to move into our sanctuary. I thought nothing of it when I entered and sat down, but then over the next hour or so I found myself frequently looking at the doors, thinking about exit paths, looking to see where Tom the army vet was sitting 'cause I knew he'd have good instincts, wondering how much noise the staff member at the building door could make, and stuff like that. Rationally I knew that I should be more worried about lightning strikes out of the clear blue sky than somebody bursting into our sanctuary exactly a week later to try again, but the rational part of the brain doesn't always get to drive.

If that happens again, how can I handle it better? Is there something I can do to help rational-brain take control from reactive-brain, or should I try to soothe reactive-brain by actually being careful about where I sit and planning exit paths so it'll stop worrying and let me pray, or what?

When we got to the Kedusha (this is the "God is great and in charge" part, and is something over an hour into our service), I found myself thinking "whatever happens, happens; I'm not in charge". Things were better after that.

I don't consider "don't go" to be an option; in addition to the fact that this is my community, this is what I do on Shabbat, and I don't want to be pushed out, I also suspect this is like getting right back onto the bicycle -- if you put the bike away to save yourself another fall today, it's just gonna be harder to get on tomorrow.

I had some active-shooter training at a previous employer, five or six years ago, but that was mostly about what to do in the moment, and did not help me plan for being, or feeling, safer in advance.

I learned that the term for what I was experiencing is "hypervigilance", and a friend helped me learn some techniques for calming it.