The natural sleep cycle makes you feel less alert in mid-day.
This period can easily be visualized using EEG measurements. In tropical countries this is the time for siesta.

The drop in alertness is magnified by a rich meal and a short nap is likely to quickly bring you back to full alertness.

replace a nap urge with press-ups. Press ups will improve circulation and raise the level of catecholamines, yet they won't budge the homeostatic sleepiness that can only be cleared effectively with a temporary transition to the sleep state!

Any suggestions?