I wouldn't worry about it. I'm not even 100% sure how the reputation is calculated. Could have just been somebody didn't like one of your posts or something. I wouldn't lose sleep over it. You'll make a comeback later on.
Reputation is just there for the sake of having it. Some people like it. I personally don't care either way. I just added it because some people wanted it. I don't really look at it much though or focus on it.