If you shoot regularly and it happened suddenly, odds are something moved on you...either your rest or your pins. If you haven't shot in awhile, it may be a slight change in your shooting form that you wouldn't notice. I wouldn't move anything yet if you don't remember bumping the bow pretty good. Try just shooting at close distances for a few days and see if your form doesn't correct itself. I know if I go without shooting for a few weeks, I always have the temptation to start moving my pins around. After a couple days the arrows start finding their mark again though.