It's the result of an inadvertent depressing of the left joystick on a XBOX ONE controller during combat. You can't cancel the animation, nor is the cancelling the sitting quick enough to avoid being killed. All I see is a sneak command for a left joystck press listed in the options under controller. I am no longer wish to burn power brews, raiding flares nor nor any other consumable.

I changed my my "crouch" control, which doubles as "sit" from default to an unused direction on my D-pad.

I'll admit I may have missed where this was described, but perhaps that "crouch" and "sit" use the same input could be listed in the control menu.