stages of sleep knowledge

For that,there are some differences between stage 4 of sleep and REM sleep.

Stage 4 of sleep which is NREM sleep, is a bit like stage 3.However, it is also a slow wave sleep which is initiated in the preoptic area and consists of delta activity, high amplitude waves at less than 3.5 Hz. The environment cannot make a sleeper wave up ,that means the stimuli of environment is not stimuli the sleeper,such as the sound of air-conditioner.It cannot get any dream but also can have night terrors, nocturnal enuresis, sleepwalking, emotions(laugh or cry) ,and somniloquy occur.

REM sleep is a way for sleeper returning back the stage of sleep 1-4. It is about muscles moving when you are sleeping that your neurons are working .It would be get a dream or nightmare whatever your body feel very tired and get the best rest.