There are five stages in the sleep cycle. These stages include non REM and REM sleep. REM stands for rapid eye movement. The first four stages of the sleep cycle are in Non REM sleep. During the fifth stage the body goes into REM sleep. The body goes through stages one through four and then backwards from four until two and then jumps to stage five for REM sleep.During the first stage your brain activity is slowed as you drift off to sleep and relaxation. The heart rate slows, breathing becomes more regular, and blood pressure lowers. In this stage a person can still be easily awakened. This is also the stage where some people experience unusual sensations resembling hallucinations. This state is known as hypnagogic and is characterized by feelings of weightlessness, floating, slipping, falling, swift jerky movements and visual images. Parts of the hypnagogic state end up fragmented in dreams and can be remembered upon awakening.
During stage two a person becomes even more relaxed and harder to awaken. This continues for stages three and four. Waking a person at stage three or four is very difficult even by yelling at or shaking the person. Stage four is where bed wetting and sleep walking usually occur. Night terrors also occur during NREM sleep. The body then goes backwards in the cycle from stage four down to stage two before entering stage five.
During the fifth stage of sleep a persons breathing speeds up and pulse rates increase. Although there are signs of active arousal in this stage the body remains paralyzed. There is also rapid eye movement and dreams occur. REM sleep is essential for learning and consolidating new memories. Nightmares can occur during this stage of sleep.
Each sleep cycle lasts about 90 minutes and a person will usually go through four or five cycles. The following is a video on sleep cycles, it may be more informative.
Huffman, Karen. Psychology in Action. Tenth ed. Jefferson: R. R. Donnelley, 2013. 174-182. Print.
Yue, Carole. "Sleep Stages and Circadian Rhythms." YouTube. Kahn Academy Medicine, 27 Feb. 2014. Web. 21 Apr. 2015.