Different exposures often result when using any of the automatic exposure modes, because the light invariably hits the scene in different amounts as the angle to the light source changes slightly each time you move the camera to take the next picture.
Below are two images taken inside the Cabelas store in Idaho. I used P-mode and auto ISO and simply overlapped two 24mm wide angle shots by. No manual exposure. No tripod. No fancy footwork required.
[Taken with Panasonic LX5.]
The two images
Two image pano (before cropping)