Roberta is startled when her 6-year-old daughter, Sally, sleepwalks into the living room. It is most likely that Sally is experiencing the stage of the sleep cycle.

Non-REM

Explanation:

Sleepwalking (also called somnambulism) is a disorder that is characterized by a person walking, talking or doing other activities while asleep.

While sleeping, humans go through several cycles of REM and non-REM sleep.

During the stage called rapid eye movement (REM) sleep, the eyes move quickly and vivid dreaming is most common.  Sleepwalking (somnambulism) most often occurs during deep, non-REM sleep (also referred to as  N3 sleep) early in the night.

Sleepwalking is very common in children and young adults than in older adults. This is due to the fact that as people age, they experience less N3 sleep.