What are the two main sleep stages?

• A. Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM) sleep
• B. Light sleep and deep sleep
• C. Awake and sleep
• D. Dreamless sleep and dream sleep

Answer: (A)

Sleep is organized into two broad categories: Non-REM sleep and REM sleep. Non-REM sleep includes three progressively deeper stages that describe how the body and brain shift from lighter to deeper sleep: a gentle transition into sleep, a true sleep stage with characteristic brain activity, and a deep slow-wave stage that is particularly restorative. REM sleep is a separate phase marked by rapid eye movements, brain activity that resembles wakefulness, vivid dreaming, and muscle relaxation that prevents acting out dreams. This two-part framework captures the main contrast: the restorative, more controlled activity of Non-REM sleep versus the active, dream-filled state of REM sleep. Terms like light sleep and deep sleep refer to parts of Non-REM stages rather than the primary dichotomy, and awake-sleep describes a state boundary rather than the sleep-stage structure.