Thanks for your advice and reassuring references. I actually stumbled upon mindfulness meditation several times on HN, and after first being repelled, I ended up up reading "Mindfulness In Plain English" recently, and now I'm about to start practicing it.
Basically, I got fed up with this state and decided to solve it once and for all. I've managed to make some progress on it and I feel better/more productive at work now, so I have high hopes it'll get even better. Mindfulness is what I'm trying now, and the next book to read is "Feeling Good" (similarly, heavily recommended on HN), a basic Cognitive-Behavioral Therapy book.