In the fall of 2018, Neurohacker Collective started to turn some of our attention to sleep and nighttime physiology. We invested time learning about changes in brain neurotransmitters that occur as we transition from daytime to night, and how these impact sleep quality. We reviewed research on the circadian system, which is essential for generating robust sleep-wake rhythms. We looked into brain energy, because while we are asleep, the brain is still busy working, and work takes energy.