Rapid Eye Movement or REM follows after the four stages of NREM (non-REM) sleep and occupies about one-fifth of total rest time in adults.
During REM, all vivid dreaming takes place. Our internal temperature is at its lowest. Our heart rate increases and our breathing is irregular. Generally, our muscles are immobilized, and we are incapable of physical response, except for our eyes and ears. However, our brain is fully active.