Thanks for giving me the opportunity to post here.
I believe I have pulled or strained my Quadratus Lumborum muscle on the right hand side... caused by hefting heavy suitcases and then sitting still for almost three hours during a plane journey!
As far as i can tell, the best thing to do is to take pain killers and stretch my right hand side while lying down on the edge of the bed - Oh, and be careful how I move until it gets better!!
If anyone has any other suggestions I'd be really grateful