It could be any or a number of things, and as people have said, will probably go away on its own in time.
However, wouldn't it be nice if you knew what caused it, and then you could nip it in the bud the next time it happens?
Ideally, you would get some coaching, either locally or from one of the many fine archery instructors who put on classes around the country from time to time, such as Rod Jenkins. Next, video yourself and send it in to the shooting form section of Trad Gang. Arne is pretty good at picking up things from videos that people send in.
Last, take your shot apart and really focus on each component, shooting at a blank bale so you aren't distracted by trying to hit anything. Common causes of slumps are failure to maintain a strong bow arm, torquing the bow or string, lifting your head (peeking) at the moment of release, failure to follow through, creeping (take a close up video of your arrow on the rest as you shoot the bow and observe whether it has any forward movement prior to release). These aren't always easy to notice. For example, if you are used to moving your head or torquing the string, it may feel natural to do those things and you have to increase your level of awareness to notice them.