I've had them seemingly stuck up in the rafters in my garage.
Even with the door up, I think that since they can't see green grass and trees, they just can't figure out where they are or how to get out, so they fly up!
I too have found them dead on the floor, sad thing!
Then I did some research and now when one gets stuck in the rafters, I go for the water hose!
Spray them with a fine spray and pay attention and after a while, their feathers will get wet enough and they will slowly lose altitude and sometimes they will glide out the door and other times, they will be on the floor, pick them up and gently brush them off and then take them outside and let them fly away!
It does work!