Chuck,
I get like that too. It's just fatigue and a little tension thrown in.... That's all.
What I have noticed (with my being lefty), is that if I accidently PUNCH the release with my index finger (major no-no [:-]), the arrow will hit the target, but be off to the right, like I caused the bow to torque somehow. If I relax and ease the release, I'll darn near Robin Hood an arrow at 20 yards!
Butch A.