Rapid eye movement sleep (REM sleep) is a unique phase of sleep in mammals that occurs at periodic intervals during the night and is characterized by rapid eye movements, more dreaming, increased body movement, an increased heart rate, and faster breathing. 

Rapid Eye Movement sleep, also referred to as active sleep or paradoxical sleep is part of the sleep cycle in which you actively dream. Your eyeballs move rapidly and randomly back and forth and the muscle tone is relaxed.

There is a physiological difference between rapid eye movement sleep and the other sleep stages, which are collectively referred to as non-rapid eye movement sleep (NREM).

REM and NREM sleep alternate with each other within one sleep cycle, which lasts about 90 to 110 minutes in adults. As the night continues, the duration of the REM stage increases. 

How much REM sleep do you need?

The average healthy adult requires and gets about 1 to 2 hours of deep sleep in an eight-hour night sleep. A good amount of deep sleep is good for your immune system. Deep sleep is the third part of your NREM sleep.

Getting the required amount of REM sleep is good for your brain. The brain is very active during this sleep, but at the same time, the body is very inactive. Actually, it’s so inactive, you’re almost paralyzed.

In most human adults, this sleep stage accounts for 20% to 25% of the total sleep time. If you sleep for about 7 to 8 hours, you spend about an hour and a half in this sleep stage.

This stage occurs about 70 to 90 minutes after falling asleep. It is characterized by high-frequency low amplitude alpha waves on EEG.

During the first sleep cycle, this sleep stage is shorter with more time in deep sleep, but as morning approaches, it becomes longer and the stages of deep sleep become shorter.

Each subsequent sleep cycle, therefore, has more REM sleep and less deep sleep. Deep sleep is the third part of NREM sleep.

During the first sleep cycle, REM sleep typically lasts for only 10 minutes, while in the morning during the last cycle it may last for 90 minutes.

What happens during REM sleep?

During the stage of rapid eye movement sleep,

  • Brain activity is increased and researchers found activity in areas of the brain that control sight, touch, hearing, smell, arousal, transitions from sleep to wakefulness, and balance and body movement.
  • You dream actively and may not remember the dreams in the morning when you wake up.
  • Sensory information about the outside world is shut off.
  • There is rapid back-and-forth movement of the eyes.
  • Breathing is shallow, irregular, and faster than normal.
  • Heart rate and blood pressure increase.
  • Arms and legs muscles are temporarily paralyzed with loss in muscle tone (REM atonia)
  • Men may experience erections during this stage.

The brain activity in this stage is quite intense and is as much as it is during waking hours. Because of this paradox of voluntary muscles becoming paralyzed in spite of increased brain activity, REM sleep is also called paradoxical sleep.

REM sleep paralysis is caused by the release of glycine, an amino acid, from the brain stem into the motor neurons.

Motor neurons are neurons, which send impulses from the brain or spinal cord to the muscles of the body. This is probably nature’s way of ensuring that we do not act out our dreams.


Rapid eye movement sleep is important to preserve long-term memories. If a person is awakened during this stage, the next sleep does not follow the normal pattern but begins with this sleep stage itself until the previous night’s lost quota is made up.

Its function is still not clear. Only theories abound.

Just as deep sleep rejuvenates the body, REM sleep refreshes and renews the mind. These sleep stages are longer in the morning and therefore try to prolong sleep a little extra without disturbance in the morning.

  • This stage plays a key role in learning and developing, improving, and consolidating memory.
  • It builds up and processes the information gathered.
  • Neural connections are formed, which strengthens memory.
  • A good sleep during this stage maintains the supply of neurotransmitters such as serotonin and dopamine, which helps to give a boost to your mood during the day.

In short, getting sufficient REM sleep is good for your intelligence. As Michael Grandner, MD, director of the Sleep and Health Research Program at the University of Arizona in Tucson puts it “If deep sleep is about the body, REM is about the brain,” 

What factors influence the onset and duration of REM sleep?

The duration and quickness of the onset of Rapid eye movement sleep depend on physical and psychological factors.

  • People who sleep less or are sleep-deprived move faster to stage 3 of NREM sleep and REM sleep than people who sleep well.
  • People who suffer from depression have a shorter duration of this sleep.
  • Depressed people who take treatment for their depression with antidepressants like Prozac have longer REM sleep.
  • In people with this REM sleep behavioral disorder (RBD), there is a delayed onset of rapid eye movement sleep and the muscles do not get paralyzed. Such people, therefore, often tend to act out their dreams, which are intense, vivid, and violent. Such actions include talking, yelling, punching, kicking, jumping from the bed, grabbing, etc. The acute form of such cases may be seen in narcolepsy, alcohol withdrawal syndrome, and in patients on sedative-hypnotic drugs. REM sleep disorder is more common in middle-aged to older men.
  • Sleep disorders such as obstructive sleep apnea and narcolepsy may fragment your rapid eye movement sleep period.
  • Babies and small children have the highest proportion of REM sleep. A newborn baby spends more than 80% of its total sleep time in this sleep stage. This proportion decreases with adolescence. Old age is associated with the lengthening of REM sleep.

Effects of lack of REM sleep

Sleep deprivation disorders, in which you are deprived of proper sleep, can lead to a total lack of REM sleep.

Since a lot of your cognitive functions are associated with rapid eye movement sleep, lack of this sleep can have a negative impact on these functions. Lack of this sleep harms the ability of a person to learn and grasp new things. It can also adversely affect your performance, mood, and health. Lack of this sleep stage sleep has been linked to an increased frequency of migraine headaches.

In children and adolescents, long-term sleep deprivation and reduction of REM sleep have been seen to cause weight gain