*reverse akshuly*
Sleep is also known as the 'little-death' because it is a reference to how sleep and death are so alike. For example: the Greek gods Hypnos (sleep) and Thanatos (death) who, in the Greek mythology, were brothers. In other mythologies, sleep is just a taste of what Death is like, a weakened version, if you will, due to their similarities. Unawareness, immobility, rest. There's tons of poems and paintings based off this idea, too.
Many of them have things along the lines of Death telling a soul that they have experienced a small death many times over in the form of their brother, Sleep, and that there is no reason to fear Death, for Death is like Sleep, only bigger.