My reputation was 310 some days ago. I did not down-vote anyone's answers recently and I'm quite sure that no one down-voted my answers or questions as there were no records about them in my user page. I don't think there was a serial up-voting problem also. But my reputation has decreased to 304 now. I don't know how this has happened.
However it is interesting to note that it has not decreased suddenly to 304 but gradually in steps of 2. The same thing is happening to my Electrical Engineering Stack Exchange account also (reduced from 254 to 252). What is the cause for this strange happening?