After lunch or right after the middle of the day students begin to feel sleepy, and a need arises to have them move around a bit to help them wake up and refocus for the rest of the day. Depending on the content you are addressing, you could incorporate a physical activity that supports your lesson.
For example, if you are addressing units of measure, you could have your students measure items around the room as an activity. If you are working on geometry, you could have students identify right, obtuse and acute angles, squares and other shapes around your classroom. In grammar, you could have students act out prepositions like over, under, below, above and so forth. If you teach a language class, you could have students label items in the classroom. With older students, you may have them interview each other for a writing assignment or even pair them up to discuss content, teach one another content and self-assess their work.