kinds of sleep: active sleep and passive sleep. The passive sleep gives our body the rest that's needed and prepares us for active sleep, in which dreaming occurs.
Throughout the night, people alternate between passive and active sleep. The brain rests, then it becomes active, then dreaming occurs. The cycle is repeated: the brain rests, then it becomes active, then dreaming occurs. This cycle is repeated several times throughout the night. During eight hours of sleep, people dream for a total of one and half hours on the average.
