In Stack overflow you can browse your reputation history at tab=reputation
.
But I don't think it includes reputation lost to downvotes. I am asking this because my reputation has decreased by 2 points last night and I cannot figure out why.
Maybe when I was using my tablet, which I am not very comfortable with, I downvoted some posts without noticing it.
Is there a downvote history tab? If not, I think it would be a good idea implementing one, and make it easier to remove your downvotes once someone edits his questions or answers.