Sleep, particularly slow-wave sleep (SWS), is critical for optimal cognitive functioning and health. Sleep disturbances are highly frequent in our society and strongly influenced by cognitive factors, e.g. thoughts, rumination, imaginations and intentions. However, the mechanism of how cognition influences sleep architecture is not yet understood. To explain how cognition influences sleep, I propose the “Memories-of-Sleep” (MemoSleep)-Hypothesis. The hypothesis proposes that the influence of cognition on later sleep relies on a repeated reactivation of pre-sleep appraisals, containing the perceived and evaluated content and its associated embodied representation during sleep. In my talk, I will explain the rational of the MemoSleep-Hypothesis, and present and discuss recent experimental findings.