@SpartanMaker is correct. It will likely be from the surgical gas rising behind the lungs & putting pressure on the phrenic nerve. From here it is absorbed into the lungs & you breathe it out. You donโt burn or fart it out.
Yes walking helps as does slow deep breathing, marching on the spot (even seated ones), lifting your arms up and down as they help you breathe it out more quickly. A heat pad can help with the shoulder & neck pain. Otherwise itโs just a waiting game. I think it took up to a week for it to abate after my gall removal surgery (I had none with my sleeve).
In saying that I had a muscle spasm in my back (I have a weakness there thanks to oozy discs) on day 2 or 3 after sleeve surgery. My surgeon suggested it was likely stress I was holding from the surgery. I had a lot of pain when swallowing due to swelling & I know I was holding myself tightly every time I had to sip or take a tablet. The spasm passed later that day.
If it persists fir more than a week & isnโt lessening, contact your team.. All the best.