Yes, I saw the scan this time and there is a line along the entire edge of the retina, outside my field of vision, and she said that's where it is starting to detach. They said the flashing is caused by it starting to stretch and tear
Surgery solved the issue on the other eye, so hopefully will be fine on this one as well.
I listen pretty loud, but not loud enough to knock an eye loose
Interesting factoids I'm finding: Retinal tears occur in 7-10% of all people, but actual detachment affects only 1% of those people. Wonderful to be one of the lucky ones.