I have almost had that problem.....

A few years back in Illinois.......very cold morning..... After sitting motionless for 3 hrs, a nice buck comes and offers me a shot at 10yds.. I draw back easily but as i settle into anchor, my arm gives out and I completely collapse all the way back to brace..... The bucks sees this movement and prepares to bolt..... I yanked that baby back as fast as I could, top pin on his heart and release..... I got lucky, but it almost cost me a nice buck!