Sally
You was right to have a look, they sleep at really odd angles at times. If you do find one cast, with all 4 legs in air, they will lay very still if they have been there a fair while, just turn them downhill. Nine times out of ten they try to get up uphill and it doesn't work. If they are o.k. they will get up have a shake, do their business and then walk off to have something to eat.
Sheep are funny creatures.