REM Sleep
REM Sleep is the deepest possible level of ordinary sleep and involves complete disengagement of the body and brain's motor cortex functions from the neck down and suppresses the left brain hemisphere functions.
The REM phase is also known as paradoxical sleep (PS) and sometimes desynchronized sleep because of physiological similarities to waking states, including rapid, low-voltage desynchronized brain waves. Electrical and chemical activity regulating this phase seems to originate in the brain stem and is characterized most notably by an abundance of the neurotransmitter acetylcholine. REM and non-REM sleep alternate within one sleep cycle, which lasts about 90 minutes in adult humans. As sleep cycles continue, they shift towards a higher proportion of REM sleep. The transition to REM sleep brings marked physical changes, beginning with electrical bursts called PGO waves originating in the brain stem. Organisms in REM sleep suspend central homeostasis, allowing large fluctuations in respiration, thermoregulation, and circulation which do not occur in any other modes of sleeping or waking. The body abruptly loses muscle tone, a state known as REM atonia.
Lucid Dreams
Rapid eye movement sleep (REM) has since its discovery been closely associated with dreaming. Waking up sleepers during a REM phase is a common experimental method for obtaining dream reports; 80% of neurotypical people can give some kind of dream report under these circumstances. Sleepers awakened from REM tend to give longer, more narrative descriptions of the dreams they were experiencing, and to estimate the duration of their dreams as longer. Lucid dreams are reported far more often in REM sleep.[1]