I don't know where I learned to fall but I am pretty good at it.
I mean the way I turned yesterday's, tripping over a bit of rubbish in the garden, into a roll rather than thumping down and lying there. I have to believe that my right side, first point of contact, hurts less because I rolled.
But what I was getting to, I experienced that real 'the air was knocked out of her' feeling. For a couple of micro seconds I was literally gasping for air.
Afterwards I thought, so that's what we mean when we (glibly) write that? I say 'glibly' because we often write things without having experienced them, and so don't really know what they feel like.
Mind you, before I became a writer, I may not have had the words with which to describe experiences and so couldn't save them to use them at a later date anyway. Because that's the worst about us writers. Everything becomes grist to the mill.