The Difference Between REM and NREM Sleep

Everyone needs sleep to restore our bodies and energy. Sleep is prompted by two natural cycles of activity in the brain that consist of two states, being rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep. During sleep, the body cycles between these states, typically beginning with a period of NREM sleep followed by a shorter period of REM sleep.

NREM
 There are 4 stages within the NREM sleep period. Each stage can last from 5 to 15 minutes, and a completed cycle progresses through all the stages followed by an REM sleep period.

• stage 1 : sleep readings show a reduction in wakefulness during this stage. A person can be easily awakened from sleep, and feel as if they did not sleep at all. This stage can last from 5 to 10 minutes. It is common to have the sensation of falling during stage 1, which causes sudden muscle contractions.
• stage 2 : this stage is a period of light sleep, in which sleep readings show intermittent negative and positive waves. These waves show periods of muscle tone and muscle relaxation. The heart rate slows and body temperature decreases. The body is preparing to enter deep sleep. 
• stage 3 & 4 : these stages are known as slow-wave, or delta, sleep. They are the deep sleep stages, stage 4 being deeper than stage 3. If a person is awoken during these stages they will feel disoriented. 

          The body repairs and regenerates tissues, builds bone and muscle, and sometimes strengthens the                 

           immune system during deep NREM sleep. 

REM

REM sleep usually occurs 90 minutes after sleep on-set. The first period of REM sleep generally lasts 10 minutes, and each recurring REM stage lengthens, making the last stage up to an hour long at times. Sleep readings show that brainwaves during this stage are that of brainwaves during wakefulness. Heart rate and respiration speed up and become "erratic". As explained by the name, this sleep stage includes rapid eye movement, in different directions. REM sleep is sometimes called paradoxical sleep because it is a mixture of brain excitement (intense dreaming) and muscular immobility. The percentage of REM sleep decreases as we age, just as the amount of deep, NREM sleep decreases as we age as well.