I believe that feeling is decompression and depending on your body different positions will decompress the spine and thus feel good

It probably depends on your specific physiology and also what you’re doing all day

I highly doubt it’s bad for you to temporarily lay on your stomach. Like any posture you should shift position somewhat often just to relieve and shift around the compressive forces on various parts of your body.

For example, I know someone who sat cross legged for too long and it compressed a nerve in their ankle causing permanent nerve damage.