Isn’t it funny that although everyone sleeps, it is difficult for us to define precisely what sleep is? Try asking people randomly what sleep means to them, and you will get different answers. When I ask my son, what sleep is, he replied, “you know what that is.” I told him I’m curious about what it means to him, so I insisted that he give me a simple definition. He said,” sleep is when people close their eyes at night and dream." My other son replied, “sleep is a brain charger.”   But really, what is sleep, and why does this happen repetitively?