a state of sleep characterized by four stages that range from light dozing to deep sleep; 75% of sleep is spent in non-REM sleep. In stages 3 and 4 of NREM sleep, there is a decrease in blood pressure, muscle activity, and respiratory rate as the sleeper relaxes.
Sleep that has little or no dream activity and is characterized by slow brainwaves. This normally makes up around 80% of a person's sleep.
Non-REM sleep - a state of sleep divided into 4 stages. These stages progress in a cycle from stage 1 to Rapid eye movement sleep, then the cycle starts over again with stage 1. Each stage represents a different physical and mental state of the body during sleep.