Just while standing...just started...just strange
So I'm standing casually in my house, did absolutely nothing, and suddenly my lower back just above my hips (or just at the top of my hips) but centrally (above the coccyx?) starts to tighten up. A few seconds later, that deep interior pain of backache sets in...but only while I'm standing. Any other position, including fully doubled over with my knees to my chest, feels fine. Just standing. Not debilitating, but definitely painful and uncomfortable enough that I can't walk very far.
Any thoughts on causes?