Four sleep stages are identified, stages one and two which can be described as sleep's lightest forms as temperature rate, heart rate, breathing rate, activity of the brain and blood pressure start to decrease. Stage three is an even deeper phase where hormonal growth is discharged for growth, repair and most importantly recovery after strenuous activity. The fourth stage is known as REM (rapid Eye movement) sleep: the stage of great allure where dreaming is most common and the brain is incredibly active. This stage is very important in terms of a person's memory and learning capabilities. It is normal to cycle through these 4-5 stages several times within a single night.