Lost one today

I found one of my hens dead this afternoon- a 2-year old silver laced wyandotte. Found the bird flat on her back on the floor of the coop. It looked like she had died overnight and fell off the roost. I've been raising chickens for a few years now, and this is the first one that has died from something other than butchering.

I'm sure any number of things could have happened, but I'm curious. Any ideas? The rest of the birds seem fine.