Sleep is a behavioral state identified in all animals so far, fulfilling a large part of their lifespam. While sleep is likely vital, it remains mysterious regarding its role and function, as why dreams populate our nights. Furthermore, it becomes even more complex in mammals, birds and humans, with two distinct states of sleep identified at physiological level: slow wave sleep (SWS, also named non-REM sleep) and paradoxical sleep (PS, also coined REM sleep). SWS is characterized by slow frequency EEG while PS is defined by waking-like low amplitude activated EEG paradoxically associated to a paralysis of skeletal musculature, with few remaining active muscles controling movements of eyes (REM) or whiskers (in rodents).