What is the term used to describe the first four stages of sleep?

Question

Quizplus · Accepted Answer

The first four stages of sleep are collectively known as NREM (Non-Rapid Eye Movement) sleep. REM sleep (Rapid Eye Movement sleep) is a distinct phase that follows NREM sleep, characterized by rapid eye movements and vivid dreams. Sleep spindles are a feature of stage 2 NREM sleep, not a term for the stages themselves. Paradoxical sleep is another term for REM sleep, due to the paradox of the brain being highly active while the body is essentially paralyzed.

What Is the Term Used to Describe the First Four