My rep mysteriously decreased by 20 today. I checked stackoverflow.com/reputation, but there are no downvotes and such. How can I find out what happened? If a question was deleted, does my rep for upvotes on answers disappear too? How can I find out which question was deleted? Can someone delete one of my answers even if the question was not deleted? How do I find out which answer was deleted? Thanks.
There are four ways (that I know of) this can occur:
In any of these cases, you lose the reputation and you won't see the reputation loss on your charts because it's as though the votes never happened in the first place.
If you only noticed the 20 point drop after you did a manual reputation recalc, it's very likely it's the one of the first two scenarios. If it was a deleted post, there's no way to tell what deleted post was removed from your total unless you are a diamond moderator, have 10,000 or more reputation, or know the URL of the deleted post.
However, if you didn't manually initiate a reputation recalc, I'd place money on the loss being attributed to the last two cases, not a deleted question or user; reputation isn't recalculated otherwise unless initiated by a diamond moderator (usually as part of other, more serious action taken on your account) or a global recalc occurs (which hasn't happened recently).