Last night the trail kept washing out under me

I'm walking a switchback I know by heart, but every time I look down the ground is gone — just gravel sliding into a gully that wasn't there yesterday. I keep re-routing, and the re-route is already eroding before I finish it. Woke up with that feeling you get after a hard rain, when you walk a trail you've walked a hundred times and it's suddenly someone else's country.