Shooting Form?

[ALDO]

I have been reading alot of the post on shooting form and have picked up some great info, thanks.  My issue is after shooting awhile it seems like all of a sudden my shots go left of what I am aiming at.  I am a right handed shooter, and shoot a 58" hybrid style longbow.  I can be at a 3D shoot and shooting great, putting arrows right where I am looking and then they start to go left.  I can't determine what I am doing it happens at my home practice range as well.  Can you give me some ideas what to look for?  If you need more info let me know.
Thanks
ALDO

[Terry Green]

Probably lack of back tension.  If I throw one a bit left, that's usually why.  You might be fatiguing as you shoot, loosing your proper alignment.

[ALDO]

Thanks Terry, I will keep that in mind next practice session.

[BLACK WOLF]

Your follow through is a great indicator of what you did right or wrong.

If your accuracy is sufering AFTER you have been shooting for a while...it's prpbably do to fatigue and you either aren't getting proper back tension or maintaining the proper tension in your bow arm and bow shoulder.

Ray  

[ALDO]

Appreciate the suggestion Ray, I will be at it again today and will see how it works out.   I did a lot of shooting between Sat and Sunday this weekend and the fatigue thing may be accurate.  
Thanks
ALDO