Resting brain
I taught in middle school in Africa for several years and discovered that when the student were getting squirrely that if we got them up and out of their seat and had them sing a nonsense song they could again concentrate for another hour. I tried this with a university group and it work just as well.
I once taught an evening class and saw how exhausted and inattentive there were after the first 50 minutes of the class. So I sent them on their 10 minute break and when they returned, they didn't seem any more attentive. So I beat a rhythm on my desk and asked them to repeat it. I did this for about 3 minutes and every student seemed to have perked up and they were all smiling. During the next 50 minutes of teaching, they all seemed to be paying better attention.
Yes, for me I am very sensitive to students who seem uninterested or simply fatigued during lecture. Having the ability to reference a topic of interest that is recent really helped me out with this. I teach in San Diego and being able to say something about the Chargers football team often gets students excited about how much they love, or in some cases hate, the team. Of course, getting back on track can be a challenge at times, but at least the students are more energized and usually that energy can transfer to the topic of lecture.
Getting students involved in group work (versus listening to a lecture) also keeps the students' brains active. I try to implement transitions within my lessons regularly. Initially, it takes awhile to create an effective lesson plan with multiple activities, but once it is complete, it is well worth it (to both the instructor and the students). Not only are the students' brain kept active- so is mine. They don't have time to get bored and I get to move around a lot too!
I also do something similar if it just seems that the students are just not "present" or if they seem overwhelmed - sometimes just getting off topic for a few minutes really gets them back on track
