Lying down pose reference
Real photos of people lying down: on the back, on the front or on one side, on grass, floors and beaches.
Lying poses are hard to stage for yourself and rarely show up in a plain image search. Each photo opens in the pose search, where you can find more like it.
Angle Ref has 232 photos like these, all openly licensed and credited.
Search lying down poses in Angle Ref
Lying down poses
Eugene Chystiakov, Unsplash License 
garryknight, CC BY Brock Wegner, Unsplash License 
Elvert Barnes, CC BY Baylee Gramling, Unsplash License Michael McAuliffe, Unsplash License Kaitlyn Pixley, Unsplash License Evita Tomševica, Unsplash License Ruslan Zaplatin 🖤, Unsplash License Zulfugar Karimov, Unsplash License 
bigredpenguin, CC BY Brooke Balentine, Unsplash License Luiza Braun, Unsplash License Renzo Alarco, Unsplash License Kenneth Schipper, Unsplash License Ingo Doerrie, Unsplash License