I found in myself that sleeping 40min. or more will trigger regular sleep cycle. In this place I was, I ate at noon in a 2 hour break period starting at 12pm, relaxed a bit and share talks with others in same dwelling then sleep for 30min. which is easy to wake up by that time and return to work afterwards, I found myself with more energy and renewed. The experience I just described is a Siesta and the "power nap" serves the same purpose so