Have you ever sat down at your organ/keyboard and just "ad libbed" ... ie. played what came into your head as you went along? Not the same as a 'Composition', as that has a deliberate structure which can be repeated. If you haven't got the RECORD button on while you are doing it then what you have played is lost for ever.
Here is a piece by John Traves (JPT) where he has done just that.
My Funny Valentine
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https://app.box.com/s/bu03d9ou72cq38ld11zxmyzgccrvhr6l