How many stages are typically recognized in non-REM sleep?

Non-REM sleep is divided into stages that reflect increasing levels of sleep depth. Traditionally, there are four recognized stages of non-REM sleep. These stages are categorized based on the brain activity and physiological changes that occur as a person progresses deeper into sleep.

The first stage is light sleep, where a person can be easily awakened; the second stage involves further relaxation and a decrease in heart rate and body temperature; the third and fourth stages are characterized by deep sleep, known as slow-wave sleep or delta sleep, which is crucial for physical restoration, growth, and healing.

It's important to note that as research in sleep continues to develop, the classification of sleep stages can vary slightly, but the four-stage model remains widely accepted in the field of sleep psychology. This understanding underscores the essential nature of these sleep phases for overall health and well-being.