Back Pain after a few hours of sleep

I started having back pain in my middle upper back after about three hours of sleep a few weeks ago.  I can't sleep laying flat anymore.  I have to fall asleep in bed only to be awaken in pretty moderate pain in my mid upper back.  I then go downstairs to my recliner to sleep the rest of the night.  When I sleep in the reclined position the pain goes away.  I don't have pain when I am up and moving.  I work in an industrial manufacturing plant and am on my feet all day on concrete floors.  Does anyone have any suggestions or ideas as to what may be  the cause of this.  It's getting to be a nightmare at night.....