Your back quite literally supports you in everything you ever do, always. One of the best things you can do for your back is simply lie down for 10mins. (Unless you are heavily pregnant).
In most cases the back will be functioning under a lot of pressure from muscular misuse in relation to gravity. When you lie down you remove the compressive force of gravity on your spine and the need for your muscles to be supporting your weight.
With the absence of pressure, the discs will reabsorb fluid from the surrounding tissue, plumping up, and the deep muscles will be able to rest.
If you allow your back to recover like this you should feel more energised and comfortable.