I went through your overview page, and it all adds up to 22 as far as I can tell. My suspicion is that somebody downvoted content of yours that you thought was so old nobody would look at it again. You have several old comments at -1.
That makes me about 99% confident that someone actually walked through my 16 comments and 2 submissions, and downvoted every single one.
The two submissions are in the main section, where votes are worth 10 karma, so 2 downvotes on those and 2 upvotes on comments would account for it.
But once in a while it does happen that someone throws a passive-aggressive hissy fit and downvotes a bunch of someone's comments. It doesn't matter. The karma will grow back.
Wait, what? But I submitted them to Discussion! They are totally unsuitable for the main site! Now my theory doesn't sound very probable…
I was misinterpreting things, or the site is misinterpreting them to me. When I search your history and click on one of your top-level postings, in the resulting window the word "MAIN" is highlighted and "DISCUSSION" is not. But further tests show that this is always true, whichever section the post was in.
Got it. The site is misinterpreting my post to you. My post is accessible through two urls: the main one, and the discussion one. (This is the case for every discussion post, including here). As it happens the links you clicked on use the main section url.
Besides the duplication of resources, using the main url when the discussion one is meant is misleading. Bug for the site redesign, I guess? (Edit: done) I also dare not test if my karma goes up 10 point if someone vote for it through the main link. (But I think such hijacking is unlikely)
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).