Today I sat for about half an hour. Towards the last couple of minutes (maybe 5 minutes or so), my mental state suddenly shifted from what it ordinarily is during zazen to one of complete and utter panic. I sat with the panic, but it still deeply shook me.

I was wondering, is this a common occurrence for any of you? Is it at all unusual, or simply another aspect of sitting that usually comes up at some point? If it isn't, any ideas about what it might mean? I suspect it might reflect some long-repressed emotion coming to the surface (as has happened to me before in the course of sitting), but it was just a generalized feeling of stark raving terror instead of an insight about something.

Any thoughts?