[larsdangly]

I think the most parsimonious solution is to declare standing up to be an action that is only permitted to combatants who move 0 or 1 hex per turn (and, obviously, who start the turn on the ground). That slots it neatly into an existing category of actions, and gives high DX foes a chance to take their shot. If someone takes the 'move 1' option, presumably that is someone rolling or crawling a meter or so as they get up.