Circadian Backflip. means: Your body’s circadian rhythm determines when your body performs certain functions, such as secretions, sleeping, awakening, temperature fluctuations and so on. But most importantly, it also dictates when those activities occur. The circadian backflip, which shift workers or people on night shifts experience when they awake after darkness falls and fall asleep after sunrise, is what shift workers and those stuck on nightshifts call it. (in Community Dictionary, added by Cael Snow)