Where the pain sits tells you almost everything
Muscle pain from a strain or a bad night on the mattress sits low, in the lumbar region, often spreading into the glutes or thighs. Kidney pain sits higher and to one side, in the flank: the band of flesh between the bottom of your ribcage and the top of your hip. Press your fist into that area on either side of the spine. If the tenderness is there rather than in the lower lumbar, the kidney is the more likely source.
