Hard perfectly flat sleeping surfaces with just a simple blanket for warmth can stimulate the lymphatic system much like a massage can. The worst is when you h

Hard perfectly flat sleeping surfaces with just a simple blanket for warmth can stimulate the lymphatic system much like a massage can. The worst is when you have an uneven surface, like when camping and there is a rock which even your (inflatable) roll mat cant dampen out, that makes sleep difficult.