power nap 
noun
A short sleep taken during the working day in order to restore one’s mental alertness.Clive, his face still damp, is soon catching a ten-minute "power nap" amidst the clutter....
- Sleep is the new 21st century status symbol, epitomised by the " power nap ".
- Body temperature falls to a daytime low in the early afternoon, making you feel sluggish - prime time for a power nap.