You could have gotten tired, attempted to rip it back to a complete full draw, and, in the process, overdrawn the bow and rapidly sunk forward and completly collasped at release, causing the bow arm to jerk wildly. When I was trying to increase my draw length once upon a time, I continually suffered this malady; I was drawing back so far that I literally ran out of expansion. I had no place to go, in terms of rotation, and could only sink forward, which I did, a lot, resulting in bad releases and my bow arm flailing left or jerking right. It also played hell with my nose. Thanks to Arne, I have accepted that my natural rotation into anchor is what it is, and I'll live with that draw length, as it results in accurate shots, albeit less velocity.