Journal of Neuroscience report of rat studies: In the initial stages of sleep, energy levels increase dramatically in brain regions found to be active during waking hours. Adenosine triphosphate (ATP), the energy currency of cells, was found to surge during non-REM sleep. This surge of cellular energy may replenish brain processes needed to function normally while awake. Sleep appears to be necessary for this energy surge to occur. So, are you making sure your brain receives enough sleep?