Hard to say honestly, too many variables. If your diet wasn't as good before, or you were overtraining, or not getting enough sleep, could all affect your strength.
I haven't seen anyone here talk about it yet, but I periodically do a deload with my training. Whenever I'm feeling beat up and not getting stronger I go half weight on all my workouts and the following week I start pushing it hard again with the heavy poundages. I always come back stronger that way and any nagging pains typically subside. It's a principle that a lot of powerlifters follow, including the westside barbell crew, although their deloads are a lot more complicated than what I do.