“Half an hour of the Jesus prayer is worth as much as three hours of deep sleep. The Jesus prayer, once it has reached a certain level, rests and calms us. So, even from this point of view, it is an invigorating physiological remedy. We may be too tired to read prayers or read Scripture, but we often have the strength still to call out, “Lord Jesus Christ have mercy on me” again and again. And doing so, Christ comes to us, calms us, and refreshes us.”
(Metropolitan Hierotheos Vlachos, ‘A Night in the Desert ‘)

http://www.europemedicaltourism.com/sites/default/files/styles/photo_gallery/public/photo-gallery/athos_2.png?itok=L9V5k3RS