Good sleep means waking up without an alarm refreshed and ready to face the world. Good sleep means waking up with less physical pain then when you lied down. Good sleep usually means there was a vivid, but unimportant, dream. Good sleep means I stayed on my back the whole night, and woke up in the same position I went to sleep in.
When I was younger I forced myself to learn to sleep on my back. I can only do it with a contour pillow, not necessarily the brand name one, but any with that contour in it. I can't always do it, but when I do my sleep quality is significantly better.
yes, it happens to me most days. Except the ready to face the world part, It's usually more like waking up without an alarm refreshed, and ready to browse HN and watch youtube.
edit: the waking up part didn't happen until I started working from home. I was always over-sleeping when I had to get showered, dressed, and commute every morning.
YMMV Of course