As an undergrad, I loved "movie day" in a class; who didn't? The class got to see and do something out of the usual routine. Students still like "movie day." That doesn't mean they're slackers. It just means that a change is as good as a rest. I don't show a lot of videos in class, but there are some times when it just plain works better than more readings or more explanations from me (for example, if you're reading novels about a manufacturing process or Moby-Dick).
Even better than a movie day for breaking up the mid-semester slump--which I haven't yet seen but might be on its way--is a class in which there's a guest lecturer or student reports. A friend of mine used to refer to these as days on which you could "put your feet up and relax." Of course, I still listen, take notes, and so on. But it's a day on which someone else is primarily responsible for keeping the class going, presenting information, and asking questions. It's good for students to hear someone else's voice and respond to someone else's questions.
Last week I had a day like that: a grad student taught a portion of the work we're reading. She did a good job, and class got to hear someone else's voice, figuratively as well as literally. Since I was sitting in their midst and apparently thus rendered invisible, when she had them do group work, I was able to hear how they were talking about the work.
So: working but in a way not working. Seeing and hearing something different. It's not only better than a movie day; it's almost as good as a snow day.