I call this the laundry detergent and bleach injury - i have hurt myself similarly by carrying the jugs in separate hands to my door, then - not wanting to set them on the ground for some stupid reason - putting both jugs in one hand while i unlock my door, reulting in strains from wrist to neck. Ice, heat, and light massage help, or seeing a chiropractor. If you can remember a recent usage mistake, thats probably what it is, is how it works for me.