REM sleep, a time when the body reaches the deepest
level of relaxation, follows the 4 stages of NREM sleep.
REM sleep sometimes is called paradoxical sleep because
electroencephalographic activity is similar to the pattern
seen during wakefulness. Respiratory rate, heart rate, and
blood pressure become highly variable, irregular, and frequently
elevated (but profound muscle relaxation occurs).
REM sleep is characterized by a preponderance of vivid
dream activity. Our large muscle immobility keeps us
from acting out our dreams.