Sleep period characterized by high brain activity, with the electroencephalography waves of low amplitude, fast paced, which contrasts with a total abolition of muscle tone base and unstable vital signs (blood pressure, heart rate, breathing, temperature).

The presence of rapid eye movements is one of the common characteristics that distinguish it from the Non-rapid eye movement sleep (NREM). They are studied in the balance sheet by polysomnography snoring and sleep apnea.

There is also a reflex erection (automatic) for each period of REM.

The Rapid eye movement sleep is cyclically repeated several times during a normal night’s sleep and is a total of about 20% of sleep in adults (but much more in infants).

The proportion of REM increases with each sleep cycle during the night. In the first cycle, it may be only a few seconds while in the last cycles they can take over an hour.

Most dreams occur during the REM, which explains why we remember dreams more often in the morning.

The Rapid eye movement sleep is unique in that it is a kind of « free-wheel » of almost all large self-regulating body functions. Respiratory or heart rhythm becomes irregular (unlike NREM sleep). The body temperature is unstable (loss of reflex ability to shiver or sweat) and can drift into the temperature of the ambient environment (risk of hypothermia in the event of extreme cold).

Note that REM sleep is the phase of memorisation, and a vasodilatation accompanying REM sleep, the nose mouths particularly. If nasal obstruction was already present, it is likely to be exacerbated leading to the arrest of nasal breathing, causing sleep problems seriously disrupting the structure and quality of sleep.