Those last days, I realized I am playing "lazily" and heedlessly during timed/rated games. It means I play without really minding if my moves are good or bad, as if I don't have any desire to play chess. Which is not, eventually, the case, or I wouldn't have played any chess games at all.If you have time, please take a look to my last rated game (for example), and you will know what I am speaking about.

Has anyone experienced this situation before? And should I take a little break from chess, just to "recharge the batteries"?

That wasn't a bad game. Many of the games I've seen from players at your level are not so great. You appeared to have played a decent game, again for your rating. Taking a break from playing is something I do once a year. I teach chess in the school system so I have 5 to 6 classes made up of 10 to 20 students as well as private students. Thus, I know how easy it is to get burned out. However, before you take a break, consider when you play chess. I try not to play chess when I'm tired or my mind is preoccupied. When I do, I'm merely pushing pieces around the board without a lot of thought. So I try to play when I'm in my best mental shape. You could also take "mini" breaks, a few days here a week there. There is nothing wrong with taking a break, just make sure it is really a case of being burnt out or just being tired.

Thanks for the valuable advice Hugh_T_Patterson actually, I think I choose (almost always) the bad moment for playing chess. Once again, thanks a lot.