I've been working at getting this hindsight set and I just went to take one last shot,Well I pull back and start aiming when my arm just goes weak,No pain,no soreness,it just gave out on me,Maybe I've just over done it today.

But has this ever happend to anyone else?

Could be one of many things. You may be shooting to much. I don't know how much weight you are pulling but you could be over bowed. Your draw length could be to long, making you work harder to hold the bow. As you see, a lot of things could be a factor. Don

I have had this happen and it was from fatigue. What i do is shoot during commercials and only shoot one arrow. Because you will usually get only one shot off at a deer. So I practice making that one shot count.

Your tired when that happens. It's all about muscle power v. endurance. I work out my shoulders part to build up strength and in part to create endurance. When you get tired any amount of let off won't help. There is still tension and your muscles must have enough endurance to keep the string back. You use "explosive" power to pull it back but endurance to keep it there. Get in the gym a few days a week and work on shoulder and lat exercises and you'll see a difference.