That happened to me three days ago or so after my last top level post. At the time said post was at -6 or so, and my karma was at 60+ something. Then, within a space of < 10 minutes, my karma dropped to zero (actually i think it went substantially negative). So what is interesting to me is the timing. I refresh or click on links pretty quickly. It felt like my karma dropped by more than 50 points instantly (as if someone had dropped my karma in one hit), rather than someone or a number of people 'tracking me'. However, I could be mistaken, and I'm not certain I wasn't away from my computer for 10 minutes or something. Is there some way for high karma people to adjust someone's karma? Seems like it would be useful for troll control.

While katydee's story is possible (and probable, even), it is also possible that someone is catching up on their Less Wrong reading for a substantial recent period and issuing many votes (up and down) in that period. Some people read Less Wrong in bursts, and some of those are willing to lay down many downvotes in a row.