I had the same problem: wake up in pain after laying down for a couple of hours, and had to end up walking around and sleep on the recliner to feel better.  The only difference is that I was getting pressure pain in the upper stomach, between the ribs.  My gastroenterologist gave me a prescription to reduce acid production in the stomach and something else to protect the stomach lining while I was waiting to get an edoscopy a month away.  I was getting better day by day as I was able to sleep longer at a time.  I ended up going to  another gastroenterologist who scheduled me an earlier endoscopy and he told me that I actually had bile reflux, which is an inverse flow of my biles from the liver.   He told me to stop taking the acid reducer medications prescribed by the other doctor and just take fiber laxative supplement to help clear my intestines so that the biles from my liver would flow down instead of up, it sounded like my intestines were clogged.   Maybe the prescription medicines from the first doctor helped, maybe the biles just eventually cleared my intestines like a slow drain, and maybe my taking the fiber laxative helped keep my intestines.  I haven't had the pain since.