Sleepwalking

Also known as somnambulism, this parasomnia occurs in NREM sleep.  The sleepwalker's brain is in fact passing back and forth between sleep and partial wakefulness.  The primitive parts of the brain are aroused, but higher level cognition remains in a deep sleep state.  Many sleepwalkers will be unable to open doors, etc.  Sleepwalking is common in children and may arise from increased sleep debt as children shift from napping to one period of consolidated sleep.  Unlike popular conceptions, the sleepwalker is not in the process of acting out a dream.  (See REM behavior disorder.)

Source:

Dement, The Promise of Sleep