What are the stages of sleep? What happens during each stage

What are the stages of sleep? What happens during each stage of sleep? Why do we need sleep? What are some of the reasons that people have difficulty with sleep? Sleep often results in dreams that we may or may not remember Sigmund Freud began to analyze dreams as a pathway to the human consciousness What is dream analysis? What are your thoughts on dream analysis and its usefulness in finding out more about a person?