Afternoon slump

The dreaded afternoon slump seems to haunt me most days.

It's often the same group (thank you, timetabling) so the option of concentrating on practical or kinesthetic lessons at those times isn't open to me. I just have to cover 'dull stuff' for a fair proportion of the time as I build up the range of specialist lexis and concepts that the students need. The school thoughtfully provides water bottles and chilled water, so this should help, but most students don't bring it along anyway.

At the minute I'm stuck - perhaps because I'm suffering the same slump? I really need some guidance from a more experienced teacher.