Update: my karma is back to normal, and more. If you feel the need to compensate in my favour, don't.
I noticed that my Karma just jumped from 38 to 20, then 22, in less than an hour, with no apparent reason (votes on my most recent comments stayed rather stable). I didn't wrote any main, toplevel article, so I suppose there's something going on with the site redesign or something that is temporarily messing up Karma?
Edit: Mystery solved. (thanks Normal_Anomaly and nazgulnarsil) My Karma did jump in odd ways, in very little time, through -1 steps only (no toplevel article). The first jump went from 38 to 20, which is a loss of 18 karma points. Before I wrote this post, I had exactly 18 comments and articles here. That makes me about 99% confident that someone actually walked through my 16 comments and 2 submissions, and downvoted every single one. Weird.
The 2 Karma points I gained shortly after probably were upvotes on my 2 most recent comments (it appears I had more after that).